Heyo! You’ll have to talk to Shaxx. He has a bunch of rewards for you; you won’t be able to claim a reward if you don’t have space for it (usually emblems or ascendant shards). They’ll look grayed out but are not actually claimed. You should see a little check mark to denote that it’s claimed. Make room for those, claim everything, and you will reset your rank.

You need to go to Shaxx and claim from the row below the bounties. If you are full of prisms you will not be able to reset them until you collect them. The row has an Engram Prism x 2 Prism x 2 Enhancement cores x 2 Enhancement cores x 2 upgrade module x 3 and Exotic engram one you have collected all and the Exotic that then resets you valor.