There are holes on the dial that hold the numbers and if the number is crooked, the holes are drilled in the wrong place. Typically there are two holes per number. One can dislodge a number from the holes by gently pushing with a soft tipped tool or a toothpick. Then cut one of the feet on the number that go into the holes. Insert the number back on the remaining feet with a tiny tiny tiny amount of glue. Adjust the orientation..and done. The holes are very small so they remain hidden under the number.
Don't run, jump, or have any funny business with the watch on or the number might fall out : P