This is MS Access, right?
You may need to modify the Access program code to add another button which would launch AutoCAD itself. You can't edit a dwg in a viewer program. It looks like Access is already launching a viewer program. The dwg does not get "saved back to Access". Access merely gives you a path to the program that opens the drawing.
You can change the Access form by copying the original button and changing the name of the executable it launches to a cad editor, but I suggest adding a whole new form for editing with limited rights to it.
I can't help with the Access coding. It has been 15 years since I did any of it, and it has changed quite a bit since then.