If your viewing key no longer works, or you would like to remove an old viewing key that you no longer need, you can follow the steps outlined below:
In the Keplr Wallet drop-down menu, you will see a "Token List". Click on it.
Find the token contract that you want to remove the viewing key for from the "Token List". On the far right, you will see a trash can icon. Click on this icon to remove your viewing key.
After you click on the trash can icon, you will receive a prompt to confirm the removal of your viewing key. Select "Yes" to confirm.