Train them like any other muscle - specifically and with some sort of progressive overload. Specific wrist exercises might be wrist curls.
Indirect exercises like deadlifts, rows, pullups or farmers carries. Only problem here is that you typically dont want your grip to be the point of failure for these exercises. Like presumably you row to make your back bigger, not make your wrists bigger.
Move wrist exercises up the order on your program. 3 lazy sets at the end of a workout probably isn't enough.