Follow the below steps to close out your position/sell your instrument on the web and app platform:
Web Platform
Select the account you used to trade:
Go to your dashboard and select "Open Trades"
Select "Action" and "Close Positions"
App Platform
Select "Accounts" on the bottom menu and scroll down to the holding you would like to close under "My Positions"
On the instrument you would like to close, click the "X" next to the position
Select "Close Trade"