The first thing you want to do is check the blockchain for your transaction. If there are no confirmations, check to see if a miner’s fee was paid. If there was no fee paid or a low fee paid, you might have two options depending on your wallet:
1) Opt-in Replace-By-Fee (Opt-in RBF)
This gives you the option to resend the transaction but include a higher mining fee. This will incentivize miners to confirm the transaction for it to complete.
2) Child Pays for Parent (CPFP)
When you apply CPFP, the transaction is thrown in to a pool of combined transactions. Instead of miners confirming single transactions, they confirm groups of them that offer the highest combined fees. For more information on how this works, contact your wallet provider.
If neither of these options are available, you may have to wait for the transaction to confirm or until the Bitcoins are returned to your wallet. Until the transaction is confirmed, the Bitcoins are still in your wallet although they may not appear to be.
Some wallets will return the transaction after 72 hours. You should contact your wallet for approximate return times.