How can I change a list with checkboxes to a dropdown list using Javascript?

I am using third-party software and don't have access to edit the code on the page, but I can add in Javascript to modify the content. I'm looking for a solution that can help change this list of checkbox items to a dropdown list. I have very little previous experience with Javascript. Thanks in advance!

<tr>
                        <td class="BBFieldCaption DonationFieldCaption"><label for="PC4519_214DIV" id="PC4519_lblLgnCtl214">Time Frame of Deduction:</label></td><td id="PC4519_ParentControl214" class="taLeft"><DIV id="PC4519_214DIV" class="BBFormChecklistContainer LoginFormCheckListContainer"><table id="PC4519_214" class="BBFormChecklist LoginFormCheckList">
                                <tr>
                                        <td><input id="PC4519_214_0" type="checkbox" name="PC4519$214$0" value="PD Til Further Notice" /><label for="PC4519_214_0">PD Til Further Notice</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_1" type="checkbox" name="PC4519$214$1" value="Seahawk 3 Year Pledge" /><label for="PC4519_214_1">Seahawk 3 Year Pledge</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_2" type="checkbox" name="PC4519$214$2" value="January - Recurring Pay Ends" /><label for="PC4519_214_2">January - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_3" type="checkbox" name="PC4519$214$3" value="February - Recurring Pay Ends" /><label for="PC4519_214_3">February - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_4" type="checkbox" name="PC4519$214$4" value="March - Recurring Pay Ends" /><label for="PC4519_214_4">March - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_5" type="checkbox" name="PC4519$214$5" value="April - Recurring Pay Ends" /><label for="PC4519_214_5">April - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_6" type="checkbox" name="PC4519$214$6" value="May - Recurring Pay Ends" /><label for="PC4519_214_6">May - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_7" type="checkbox" name="PC4519$214$7" value="June - Recurring Pay Ends" /><label for="PC4519_214_7">June - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_8" type="checkbox" name="PC4519$214$8" value="July - Recurring Pay Ends" /><label for="PC4519_214_8">July - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_9" type="checkbox" name="PC4519$214$9" value="August - Recurring Pay Ends" /><label for="PC4519_214_9">August - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_10" type="checkbox" name="PC4519$214$10" value="September - Recurring Pay Ends" /><label for="PC4519_214_10">September - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_11" type="checkbox" name="PC4519$214$11" value="October - Recurring Pay Ends" /><label for="PC4519_214_11">October - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_12" type="checkbox" name="PC4519$214$12" value="November - Recurring Pay Ends" /><label for="PC4519_214_12">November - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_13" type="checkbox" name="PC4519$214$13" value="December - Recurring Pay Ends" /><label for="PC4519_214_13">December - Recurring Pay Ends</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_14" type="checkbox" name="PC4519$214$14" value="Other Pldgs Til Further Notice" /><label for="PC4519_214_14">Other Pldgs Til Further Notice</label></td>
                                </tr><tr>
                                        <td><input id="PC4519_214_15" type="checkbox" name="PC4519$214$15" value="Pre Planned Gift or Committmnt" /><label for="PC4519_214_15">Pre Planned Gift or Committmnt</label></td>
                                </tr>