These videos are demonstrating the model 3034D. The cases for the other family of Brother Serger models are physically the same - though each one may different cosmetically.
How to repair Brother 3034D overlocker serger, foot lever
This goes through how to take off the front face of the machine so you can see what the issue is.
In this video, the problem fixed is the lever that lifts the foot up and down.
The next video goes through how to put everything back together again.
How to put it back together