Trending @Cognizant; Release from a project

I am currently deployed to a project and that is not according to my choice and interest so I reached out and got an opportunity for other project that seems aligned to my interests. My new project lead asked to me get release from my current project manager. When I reached out to current project manager, they are saying until go live I have to be in this project only and then they may try to push me to another one of my choice not sure on that (even though I have just been deployed to this project may be a month and assignment end date is on june with zero dependency and no work) still they are saying this thing. What should I do? Please suggest? Is this so difficult to get tagged to a project of our own choice and the managers don’t release even with no dependency ?