It is essential that you claim your NFT on desktop first. Read more about this here. Install and launch MetaMask iOS or Android app (depending on the OS of your mobile device).
Select ‘Import using Secret Recovery phrase’ to get started.
Enter the 12-word secret recovery phrase in the Secret Recovery Phrase field, with a space between each word.
Enter a new password for the MetaMask wallet app, then click ‘Import’.
Great success, you get to see a screen saying ‘Congratulations’.
When logged in, go to settings by pressing the hamburger menu at the top left.
Go to ‘Networks’.
Click on ‘Add network’.
Add ‘Polygon Mainnet’.
Go to wallet.
And click on the tab ‘NFTs’.
Click on ‘import NFT’.
Paste the contract address (to be found at the bottom of the NFT page of your order).
Insert the ID (this is the number of your NFT, which you will receive when you’ve claimed your NFT).