To withdraw, you need to go to supplying section on the «App», select the market of your deposited asset, and click on «Withdraw». Select the amount you want to withdraw and confirm the transaction. You can also use your «hTokens» as liquidity without withdrawing.
There should be enough liquidity (not borrowed) to be able to withdraw. If there isn’t enough liquidity, you would need to wait for more liquidity to be deposited from suppliers or repaid by borrowers.