Just restart the game, if you just did the tree jump shortcut to get it. Or if you did lose the ring, then just go through the game without it. You'll be surprised on how little of use this ring becomes in a regular playthrough.
After fighting a boss, there is a slight pause before souls are dispensed to the player. As long as you equip the ring before the souls are given out, you will still get the 10% extra souls (in case you want to use a different ring during the fight with the boss).