Both phrases would be okay but neither are natural.
The phrase "Lift a finger" is usually used to refer to someone as lazy or sometimes someone may say it to someone who asks for help when they're tired. Sorry this is confusing let me give an example!
1. "The parents do everything in that house. The cooking, the cleaning, their son doesn't lift a finger."
2. "Hey could you help me with dinner?"
"After all I did today? I'm not lifting a finger"
Hoped this helped!!