How to check if an wallet address is a owner of my NFT using ERC 721 BalanceOf function?

I want to do a giveaway for my next phase of NFTs, to owners of my NFT. But I don’t know how to check if they’re are owners of my NFT. I’ve received loads of address wallets but I’ve been told to use Openzeppelin, can someone guide me. I have no coding experience and just want to make sure current holders of my NFT will be receive a free NFT from me.