Minimum spin speed increases over time while spinning. If you leave it spinning for too long, the speed will be very fast. If the current speed is too fast for you to stop the spinner accurately, you can lower it as long as long as the minimum is not equal to the maximum by using the ability with the arrow that points in the opposite direction, so if the spinner spins in the direction indicated on skill [A], use skill [S] to lower it and vice-versa.
Minimum spin speed is based on the current number of chips: if there are no chips, the minimum spin speed is 1 light. If there are 3 chips, the minimum spin speed is 4 lights (equal to the max). So, if you've left it long enough that your multiplier is 7x and you have 3 chips on the board, stop it first and lower it while you're stopped. Skills don't recharge while you're stopped, so you'll still have to spin and stop and spin for a bit before you can lower it back to 1 light.
I considered just recording a video tutorial, but I feel like players wouldn't bother to watch it anyway, and at that point, I might as well give up.