How to test validator registrations in a testnet?

I deployed flashbots relay on my local machine. When I am testing validator registration using curl -X POST localhost:9062/eth/v1/builder/validators -d @testdata/valreg1.json, gives an error - not a known validator. I tried to test this on goerli. I am not sure how to test validator registrations becuase that needs, fee recipient, public key and signature of a validator on goerli. I can find the pubkey of goerli validators, but how to find the signature and fee_recipient ? Any help is appriciated. Thanks.