Make sure to first have SuperBLT, and BeardLib installed. Click the links in the dependency list.

Optional video tutorial for installing SuperBLT, BeardLib, and mod_overrides mods: https://youtu.be/rin_sjSJIkg

1. After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
2. Navigate to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here). Create the folder if necessary
3. Move the main folder of the mod from step 1 to the folder you navigated to in step 2.

The Hitmarker "Saves" folder goes into the "mods" folder
Both the Health indicator and the Interaction circle respective folders go into the "mod_overrides" folder