If you mint the same NFT twice, and want to remove one, you can do so by burning the NFT. This means that the token you minted will be permanently destroyed and removed from the Ethereum blockchain.
You will not receive the gas fee back that you paid to mint the NFT, and you will also need to pay another gas fee to burn the copy. Each time you interact with the blockchain, you will need to pay a gas fee to the network. Be careful when you mint an NFT to avoid this in the future.