The first thing I would check is that your puppy is receiving good balanced nutrition that is allowing proper bone growth. That said...
My dog did have a tail kink at one point as he was growing, and I think it was because he used to constantly yank it to one direction playing with it. I used some unconventional methods to help it straighten, but I wouldn't advise replicating unless I'm giving thorough personal instruction because it is difficult to do safely. I don't want to recommend something tricky that causes harm when done incorrectly. In my case the tail has straightened out and now looks like a normal tail, though it retains a slight curvature in that direction. It looks completely natural now though. I believe I started working with it when he was around 6 months old.
I will include a photo I took back when it was at its worst and later after it straightened. If you want info on what I did, send me a PM.