Technically, this is how NFT Bridging works: A user deposits an NFT into a Smart Contract of Network A. The NFT gets locked. Afterwards, the user has to get signatures from the oracles who will confirm that the deposit was made in network A. With these signatures, the user can call the same contract in network B where a duplicate NFT will be minted and sent to the user. If the user wants the original on network A back, the user needs to send the duplicate NFT to the bridge (where it gets burned), ask the oracles again for signatures to confirm that it happened and then call the contract in network A where the original will be released.