How to open a bootstrap modal when checked a chec-box (when a tick is placed on a check box)

I've a custom checkbox. What I want is to to open a bootstrap modal when the checkbox is checked. I want a bootstrap modal to open just as when clicked a button. Hope you understood my question. How can I do it.

HTML CODE

<input type="checkbox" id="test7" checked="checked"/>
<label for="test7">Custom Avalability</label>
<br /><br />
<input type="checkbox" id="test6"/>
<label for="test6">Manual</label>

CSS CODE

      /*
      ----------------------------------------------
                          CHECKBOX
      ----------------------------------------------
      */
      /* Base for label styling */
      [type="checkbox"]:not(:checked),
      [type="checkbox"]:checked {
        position: absolute;
        left: -9999px;
      }
      [type="checkbox"]:not(:checked) + label,
      [type="checkbox"]:checked + label {
        position: relative;
        padding-left: 25px;
        cursor: pointer;
      }

      /* checkbox aspect */

      [type="checkbox"]:checked + label:before {
        content: '';
        position: absolute;
        left:0; top: 0px;
        width: 20px; height: 20px;
        //border: 1px solid #aaa;
        background: #09ad7e;
        border-radius: 3px;
        //box-shadow: inset 0 1px 3px rgba(0,0,0,.3)
      }
      [type="checkbox"]:not(:checked) + label:before {
      content: '';
        position: absolute;
        left:0; top: 0px;
        width: 20px; height: 20px;
        //border: 1px solid #fff;
        background: #eee;
        border-radius: 3px;
        //box-shadow: inset 0 1px 3px rgba(0,0,0,.3)
      }
      /* checked mark aspect */

      [type="checkbox"]:checked + label:after {
        content: '✔';
        position: absolute;
        top: 0; left: 4px;
        font-size: 14px;
        color: #f8f8f8;
        transition: all .2s;
      }
      [type="checkbox"]:not(:checked) + label:after {
      content: '✔';
        position: absolute;
        top: 0; left: 4px;
        font-size: 14px;
        color: #ddd;
        transition: all .2s;

      }
      /* checked mark aspect changes */
      [type="checkbox"]:not(:checked) + label:after {
        opacity: 1;
        transform: scale(1);
      }
      [type="checkbox"]:checked + label:after {
        opacity: 1;
        transform: scale(1);
      }
      /* disabled checkbox */
      [type="checkbox"]:disabled:not(:checked) + label:before,
      [type="checkbox"]:disabled:checked + label:before {
        box-shadow: none;
        border-color: #bbb;
        background-color: #ddd;
      }
      [type="checkbox"]:disabled:checked + label:after {
        color: #999;
      }
      [type="checkbox"]:disabled + label {
        color: #aaa;
      }
      /* accessibility */
      [type="checkbox"]:checked:focus + label:before,
      [type="checkbox"]:not(:checked):focus + label:before {
       outline: none !important;
      }

      /* hover style just for information */
      label:hover:before {
        //border: 1px solid #4778d9!important;
      }

      [type="checkbox"]:not(:checked) + label {
      color: #ddd;
      }