I've mentioned this in one of your earlier posts. You need to set an escape within the loop. You can do this by setting a label outside the loop and writing a GOTO to this label within your loop. E.g.:
@LOOP
IF BUTTON() AND #B THEN GOTO @OUTSIDE
GOTO @LOOP
@OUTSIDE
This will make that happen.
@LOOP
LOCATE 0,0PRINT "First screen."
IF BUTTON(2) AND #B THEN CLS:GOTO @LOOP2
GOTO @LOOP
@LOOP
LOCATE 0,0PRINT "Second screen."
WAIT 200
Change line 7 so that it's inside a conditional and prefix a GOTO to the label. Like this...
IF BUTTON(2)==#B THEN
PRINT "STARTING"
GOTO @OUTSIDE
ENDIF