How to check the state of the checkbox?

Sorry but this is not clear for me.

 

You want to examine the value of a checkbox

And if the value is checked (true) then allow user to change the value.

 

That's what you need ?

 

To ask user to set a value you can use (quick and dirty code) :

let checkboxValue = myWebObject.checked;
if (checkboxValue) {
  let result = MessageDlg("Choose value of the checkbox by hitting the Yes for true or No for False", mtConfirmation, MkSet(mbYes, mbNo), 0);
  myWebObject.checked = result == mrYes;
}