do you mean .mde?
If so, then unfortunately this is not possible, forms and reports cannot be edited in .mde as they are precompiled - you'll need to go back to the original .mdb and make the changes there.
If you do not have the orginal .mdb you might be able to find some help on the web to decompile the .mde to a .mdb but I don't know what it costs or how successful they are.
However you can edit the query if the form refers to a query as it's recordsource, but I doubt you will be able to refer to anything on the form for filtering purposes.