My relative had a blood transfusion during the surgery. so could i be able to donate blood/platelets?

Already done & yes: The operative transfusion is done. Some blood centers allow patient to have volunteers donate on their behalf to reduce the bill for the blood products (kinda by replacing the stock of them). Worth asking about, but donation is always a good thing, especially in summer months as donors go on vacation and more people get active, hurt, and need blood!