How to revoke the freeze authority

Hi i minted the NFT by using the token metadata program, and noticed that the program is using the PDA as the mint and freeze authority. Now i am trying to delegate/unlock the freeze by using unlockV1 fn. But i not sure how to pass the PDA as the authority as the fn need it as signer. I have no clue on how to make/ convert PDA as signer. can any expert please guide me? Thanks