First, download the provided modlist and save it to an easily accessible location. Then, open your Prism launcher. If this is your first time launching it, you'll need to go through the setup guide and link your Minecraft account. Once that's complete, click the 'Add Instance' at the top left. 

Next, click on the 'Import' tab on the left side. Then, click 'Browse' on the right side, then select the modlist, and click 'OK' at the bottom to begin importing it. This can take upto a minute to complete.

After it finishes importing, click on the instance once, then click 'Launch' on the right side. You're now ready to join!