How do you populate a textbox on 1 form with a checkbox label from a different form?

I have two separate forms I'm currently working on. Form 1 (Long Term Conditions) - Stores information. Form 2 - Populates with information from Form 1.

I'm trying to pull the text which sits alongside a checkbox from Form 1, to appear in a textbox on Form 2. So for example, if the checkbox for "Asthma" is ticked on Form 1, then display "Asthma" in a particular textbox on Form 2. The field name is "AsthmaID" in Form 1, but I am finding it difficult to just populate the word "Asthma" into Form 2.

    UserDefinedJavascript.DefaultFromParent = function ()
    {
        var xmlDoc = StrandXML.CreateXMLDocument (UserDefinedJavascript.DocumentSetXML);
        var LTCNodes = xmlDoc.getElementsByTagName("LongTermConditions");
        if (LTCNodes.length > 0)
    {
              if (GetControl("AsthmaID").value = "1")
    {
      GetControl("ExistingLTCs").value = 'Asthma'
      var str = GetControl("ExistingLTCs").value
      var newstr = str.replace (/<\/?[^>]+(>|$)/g, "\n") 
      GetControl("ExistingLTCs").value = newstr
    }

It would be greatly appreciated if somebody could help tell me where I'm going wrong and what I need to do, please!