There are probably 100 ways to restore a Btrfs snapshot. One of the easiest (in my opinion) is to use Btrfs Assistant. It takes care of a lot of dirty details for you, and makes the whole process extremely simple.
In Btrfs-Assistant, open the Snapper tab and click “Browse/Restore”. Make sure you are interacting with the target you want (it will be called “root”–it is most likely the only one you have in there).
Find the snapshot you want to restore by referencing the timestamp or snapshot description. The Pacman snapshots are labeled pre- and post- for each transaction (you can read that as “before I installed package foo” or “after I updated the system”). In your case you may be looking for something like “pre pacman -S xrdp”, if you installed it with Pacman.
Click the Restore button, optionally give the backup of the current state a unique name (it saves it in case you want to revert), and then reboot.
It is in your home directory. It looks like you have chosen to completely overwrite the file during this step:
In that case, you may as well just delete it and allow a fresh one to be populated the next time you sign in.
rm ~/.xsession
If you wish, instead of deleting it you can move it to a backup. This will have the same effect as deleting it but will preserve the state of the file in case you wish to refer to it in the future.
mv ~/.xsession ~/.xsession_backup
In this case it is unlikely you will ever want a backup of this file, but moving files to a backup state instead of just deleting them is a good habit to get into because it creates the opportunity to restore the file if something goes wrong.