Forge Slate 1.19 is also now out, check it out at goldn.dev/forgeslate/1.19
Installing a modpack using the Technic Launcher is easy. If you don't already have the launcher downloaded, visit our download page to get the latest version.
Type in the modpack name (Forge Slate - 1.16.5) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select Forge Slate - 1.16.5 from the list on the left. The launcher will handle everything else!