I'd try to SELL the card on EBay ASAP.
Due to the CRYPTO mining craze starting again there are RX-480's selling for $400+USD. People are buying any GCN card that is functional. Even if you sell with a bad fan you may make enough money to buy a better or similar (but new) NVidia card.
Other:
As for the FAN replacement that's tricky. You want the characteristics to be as close as possible. It's hard to answer just looking at the picture.
Your fan is I assume a 3-pin (voltage controlled) and the new fan should have similar RANGE (i.e. 400RPM to 2000RPM or whatever). You may just want to experiment and see what works.