Install the Updater with Modrinth App

Download the GR Updater Mod from https://files.thegameroom.xyz/minecraft/modded-season-2/gr-updater-mod-1.0.0.jar

From the Modrinth App, click the Menu icon next to the Modpack, then press "Open Folder"

This should open a new window with the mod instance folder. In there, open the "mods" folder.

Finally, copy the gr-updater-mod-1.0.0.jar file into that mods folder.

You can now launch the Modpack, and you should be prompted with a screen to install the latest updates to the modpack.