When you download the release, there are two files, PSFix.8bp and PSFixLauncher.exe. There are two ways to use PSFix, either as a Photoshop plugin or by using the launcher. The plugin has a limitation where OpenCL will be disabled, so if you need/want OpenCL, you have to use the launcher.

Photoshop Plugin

Simply copy PSFix.8bp into your Photoshop plugins folder (C:\Program Files\Adobe\Adobe Photoshop CC 2018\Plug-ins for CC 2018).

Launcher

Run PSFixLauncher.exe to launch Photoshop with the fix. You'll have to use the launcher every time you want to start Photoshop, if you don't want to have to do that, use the plugin instead. Note that PSFixLauncher.exe still uses the PSFix.8bp file so keep that next to PSFixLauncher.exe.