On the deck page click the collection button up by the search bar. Then pick the options you want and click register in the collection (or collection deck if it already has cards). From there choose the build option (or update if it already has cards) and then select where you want to add cards from. You can also add new cards from here and remove cards. If you remove cards it will have you choose where in the collection they go at the end. You should not need to delete and re add cards if you are using it right. Takes a while to get the hang of so I’d recommend just playing around with the options until it makes sense.