You can search through _screen.forms array which contains reference of all the opened forms.
For example

FOR lni = 1 TO _screen.formcount
IF _screen.forms(lni).name = 'AAAAA'
_screen.forms(lni)......objectreference
ENDIF
NEXT

>I have 2 forms in the screen. How I make Enabled=.T. CmdButton in the second form /back form/, from the aktive form / front form/.
>Robert