Where to add coolant?

[Gladiator]

I see that the reservior level is below "low" but when I open the coolant cap it is overfilled/ overflowing.

So I'm left wondering where do I add coolant?
Thx

[pinoyesv6]

the resovior is an overflow tank. i first check the radiator when it is cool. fill that up if needed. then if needed, fill up the resovior overflow tank.