After Sclerotherapy, will the veins come back when I use a forearm exerciser in that hand?

After hand sclerotherapy, I recommend waiting 24 h before performing any forearm or hand exercises. it is unlikely that any subsequent exercising will cause the treated veins to recur. However, hand sclerotherapy carries a small risk of new blood vessels developing in the treated area and back of the forearm as a response to treatment.

Following sclerotherapy on leg veins I recommend return to normal activities including exercise as soon as possible.  Following sclerotherapy on hand veins I recommend compression for 48 hours and return to full activities after 24 hours but continue compression

If it is for hand veins, I would wait 2 days. For leg veins, exercise immediately with walking after you get home from the procedure. I tell my patients to run/elliptical etc the next day.