Join a discord server that has sysbot. Then all you gotta do set up a trade, by uploading a mon onto the channel, and using the trade command. https://disboard.org/servers/tag/sysbot
Check the rules of the server you're joining, and check what the trade command is.
After all that, you'll be PM'd a 8 digit link code, which you can use to trade in-game.
After the trade, the mon you traded to the bot will be sent to you as a pk8.
It's really not that complex. Just have some patience and try it out :3
(Do note that for most sysbot trades, you'll need to have an active Nintendo Subscription Online)