How do I change my ai movement component from Character movement component to pawn movement component?
my game is single player and I heard that character movement is expensive
Well, if your AI bots are based off of the character class, they will have character movement components by default. If you do not want to use the character movement component, you will have to create AI derived from the Pawn class.
You can then choose to add one of the more simplified movement systems like the FloatingPawnMovement. You can call the Move to Location or Actor node on it and it should work just fine as long as you have a navmesh in the level.