Pretty straight forward once again. You can destroy cards in your possession that you don't want and get some Scrap in return.
Go to Customization or Manage Bounties and find a card you have but one you're not interested in keeping. Press
and then confirm its destruction. Repeat the process until you have enough to craft a card with low Scrap value.
I personally crafted a common Lancer skin that was worth a little more than 100 Scrap.