Swelling came back 1 month after hair transplant, what should I do?

Swelling can occur after any hair transplant procedure.  If you are concerned it is best to contact your doctor.  Swelling is NOT normal after one month.

Although swelling shortly after surgery is not uncommon, it is unusual to have it recur a month later.  You ought to call your surgeon and go in for an evaluation.

Definitely go see your doctor. No new symptoms, especially swelling, should be appearing after a month. Pretty much all symptoms should actually be gone by now- swelling at this point suggests that there may be some underlying issue that your doctor will need to address. Without an examination there's not much to make a diagnosis.