Hard to say without knowing more about your tub/shower faucet set-up. By no means are all RVs alike in plumbing!
If the pull-up is on the tub spout and the spout is separate from the faucets, you probably have to replace the spout. If it's part of the faucet assembly in an RV, it should be repairable but you probably won't find parts for it. Generally better to replace the faucet.
Exceptions to this would be if you own one of the high end brands that uses a standard Moen, Delta, Pfister, etc. tub faucet assembly. Parts will be readily available in most hardware and home stores.