How to Join a Remote Raid Party
Download the GO Raid Genie App and create an account.
Select the Remote Raid Party that you want to join.
Copy the host's trainer code.
Switch to Pokémon GO and send a friend request to the host.
Return to the GO Raid Genie app and notify the host that you sent the friend request by pressing the "I Sent the Friendship Request" button.
When the host starts the Remote Raid party, you'll get notified. When you get notified, switch to Pokémon GO and join the remote raid.
Don't forget to rate the host.
Filter
You can filter the remote raid parties you want to join by tier and Pokémon. If you do this, only rooms according to your chosen criteria will be shown on your home page.
Click the "Filter" button.
Select the Pokémon you want to display on your home page.
Click the "Apply Filter" button.
You can use the "Clear Filter" button to clear your selections.