Signature is undefined when executing sendTransaction

Hi,
I’ve encounter some issue when executing sendTransaction, when I was transferring NFT, the issue is this part which adding this in transaction, anyone can explain the correct params and where and how to get it?

createTransferInstruction(
fromAccount.address, // source
toAccount.address, // destination
tokenMintAddress, // mint
1,
,
TOKEN_PROGRAM_ID
)