You can choose to keep your NFTs in your Crossmint wallet or to send them to your own wallet, such as Phantom for Solana or MetaMask for Ethereum.
To do so, go to your profile on crossmint.io, find the NFT you would like to export, and tap the Export button. Please note that NFT exports may take 1 business day to complete.
For more information, please see the video tutorial here: https://www.youtube.com/watch?v=BxCfuu4tYgQ - Please note that this explainer applies to Solana-based NFTs (hence the use of the "Phantom" wallet, which is for Solana). In the case of NFT's in the Ethereum blockchain, you would need to use a MetaMask wallet instead of Solana one.