Can a cysts on forearm get a bit bigger and red after trauma on that cysts? pc doctor told me to wait two weeks if not improve consult general surgeon?

You can apply cold compress 2-3 times a day for a couple days. If the site gets swollen, hot and tender, superinfection may occur then you have to see your doctor. Otherwise, you should be fine and sometimes trauma makes the cyst disappear, especially if you have a ganglion cyst on the wrist.

Yes, a cyst will get bigger and inflamed after local trauma and watching it closely is advisable. Your plan otherwise is good to see if the cyst would be excisable/ removable by a surgeon.