Well, what exactly do you want the ball to do?
Do you want it to bounce in a random way, like when it hits the player paddle? or just in the opposite x value but continue the y value?
If you want a random response, use the same formula as in this section:
IF SPRITE COLLISION(player,ball)
ballyspeed# = 0 - (ABS(ballyspeed#) + speedinc#)
random# = (RND(10)-5)/10.0
ballxspeed# ballxspeed# + (playerspeed/2) + random#
score = score + 1
ENDIF
or try this if you just want it to bounce:
IF SPRITE COLLISION(platform,ball)
ballyspeed# = 0 - ballyspeed#
ballxspeed# = 0 + ballxspeed#
ENDIF
(I am assuming your ball is bouncing from left to right) if it is going from top to bottom, then just change the + and - in the code above.
Hope this helps
Happy Coding