Help with button to form relation

Hi All,

New to Service Manager.

Need to edit a form to add a new field into it.

The form open from a button click . 

The button properties is as shown below. Can somebody please help with the [$edit.rd.attach.record] .

I am bit confused ,if its a variable just used to check the condition to open the form.

Where should I search and update if I want to open another new form in place of the existing form the button opens.





Thanks in advance,