What kind of turntable do you own? Belt-drive, direct-drive, or idler-drive? I am going to guess it's a belt-drive. First, I would do nothing until you receive and install your new belt. Second, would depend upon your tt has a stand-alone motor where you can move the motor towards or away from the platter. Sometimes that is sufficient to adjust speed, although it is not intellectually satisfying. If your motor is fixed in position with respect to your platter, and if once you get the new belt your tt is still "fast", then consider a motor controller.