Enter layout mode, click the text tool (large capital T) and then click the button. As long as the button is a normal filemaker button, that's usually all you need to do. If that doesn't work, try ungrouping the button but that can "disconnect" the button from its script--so that needs to be done carefully. (You can copy the button to play with it and when you get it figured out, then do it for real on the button you intend to use on your layout.)
It's also possible to set up an inserted picture as a button. If this was done, you won't be able to edit the text, you'd have to replace the button with a new picture.
Thank You once again :) I am more and more happier using this software.