This is generic Gray Skin for MiG-21 either for AI or flyable.
Place the unzipped folder in C:/Users/your computer account name/Saved Games/DCS/Liveries/MiG-21Bis/
Note if you donot see MiG-21Bis folder in Saved Games/DCS/Liveries then create one.
If you donot see the skin in mission editor then goto weapons loadout page and sel ect India as country then select skin fr om the dropdown.
For changing the aircraft Number check the provided readme file. Enjoy!