You will need the doom eternal mod injector tool to use this. You can find instructions and dowloads on the Doom 2016+ modding discord server.
(I assume if you are downloading mods you alredy have it) If not, all instructions can be found there.

If you do not trust any of these files you can always use Virustotal: https://www.virustotal.com/gui/

If you have or already set up the mod injector:
Add the dowloaded ZIP file to your Mods folder inside Doom Eternals files.

If you want to make your own scope skin! Here is how:
Step 0: The same server where the mod injector is avalible, you will need to download the Auto heckin' scope maker.
1. Download and install 7Zip. If 7Zip is already downloaded on your PC you can skip this step.
2. Make and export a custom scope in an image editing software using the Blank Template Scope with the folder.
3. Drag And Drop the file into Auto Heckin' Scope Maker.bat.
4. A ZIP file will be made with your converted file as a ready to use mod.
5. Add you ZIP flie to the mods folder.

If something goes WRONG, not to worry just Repair/Verify files on Steam/Bethesda Launcher.
That should fix it right up. NOTE: this fix will delete your mods too you will need to reinstall them.