Go on Oasis.app/borrow and click on Connect a wallet. Select the wallet you want to connect. Click on Your Vaults on the top right of the page. Select the Vault you want to payback (if you have more than one) and click on manage Vault. Then select the Dai tab and under Payback DAI input the amount you want to pay back.
You will see the new Collateralization Ratio and Liquidation price simulated for your convenience. Then you will need to setup your Dai allowance for your Proxy in case you haven’t done so before.
Once you confirm this, the right box will allow you to review the changes to your Vault. Now you can confirm the operation. Once you sign the transaction you will only need to wait for it to be mined.
Note: in the video waiting times are shortened and they seem very short, don’t worry if you have to wait longer!