How can i add keyframe on particlesystem?

Hello guys i am quite new to blender and i want to make an animated video!
I made a fire through particle system with emitter type and set gravity to zero!
My question is how can i actually add keyframe so i can export my fire on a video format?

Press I to add the factor.

Moved from “Artwork > Animations” to “Support > Particles and Physics Simulations”