Unclaimed sends are cancelled automatically after 30 days. The money stays in your wallet the whole time, so there's nothing to get back.
To see how long is left, open the send in your transaction history. It shows when the send expires.
To cancel it sooner, open the send and tap Cancel this send.
Keep the money in your wallet until the send is claimed. If it's gone when they try to claim, the claim won't work.