This letter can be written to any higher authority to transfer any employee from one project to another. You may change the template according to your needs and circumstances.
Transfer of one Project to Another Project
Name of the office
Name of the post
address of the office
With due respect it is stated that I was working on a project on XXX but then I was transferred to Project YYY. Now, the billable time has collapsed. I was working with full dedication and motivation in project XXX. Now, when I am done with work in my YYY project. I request you to please transfer me back to XXX project because that is my field. I was very skilled at it as well. Not only that, I loved my job which included (mention your job and the things you used to do while being in XXX project)
Therefore, it is requested to please transfer me back to XX project. I will be very thankful to you. I am looking forward towards your reply. For any details please feel free to contact me.
name of employee