Go to the NFT’s page. (Note that you can only clone an NFT that you own.)
Click on the ellipses (⋮) in the NFT’s interaction box. A menu should open up, which contains possible actions. From the menu, click on “clone”.
A dialogue box will open up, where you can enter the number of copies you want for the NFT
After entering the quantity, click on the “clone” button and sign the transaction.
Wait a few seconds for the transaction to complete.
That’s it. To confirm that your NFT has been cloned, go to your NFT’s collection page and you should see multiple copies there. Essentially, the total number of items in the collection should have increased by the quantity of clones you made.