THIS FEATURE IS ONLY AVAILABLE FOR 1.39.1 AND OLDER VERSIONS.
We have a guide on how to make Atomic Swap in Atomic Wallet, you can read it here.
And also here is a small video of Atomic Swap process.
The process itself takes some time to implement due to different factors, such as - another party, internet connection and others.
In the meantime, check out our Litecoin Wallet.