I found my old antique rooster lighter xcept its out of fluid how do i put more in???

Question:theres screws on the side but on the bottom theres this circle thing

Answers:
The screws on the side are for replacing the flint and wheel. The Circle thing on the bottom is the refill port. Sometimes it is just scored so your thumb can unscrew it by pushing in and turning. Later models have either a slot for a small blade screwdriver or a Phillips.