To add these Decals to DecalMachine:

Go to Edit-> Preferences-> DecalMachine-> Import Existing

Or unzip the folder and copy it to your DECAL folder in your libary.

Take a look at the DecalMachine Docs: 

https://machin3.io/DECALmachine/docs/

To add these Decals to Kit Ops: 

Unzip the folder and copy it to your libary.

Go to Edit-> Preferences-> Kit Ops-> File Paths-> click on the plus and select the folder

Take a look at the Kit Ops Docs:

https://docs.google.com/document/d/1rUzomyTi7ec2sFqeCgyVYgkbdnmVanlDCWYcvAzxOXE/edit