The fender is one part on a bike that is not a precision part, and the answer to this question is not exactly elegant. I usually just nudge, finesse, or firmly but gently push them over into the position that is needed. In my shop days, when we are working fast, I found the most effective method was giving the fender a firm, gentle thump with the palm of my hand in the desired direction. This fixes the issue in pretty much all cases.
Of course, if this does not help or there is some other issue, we have a wide array of solutions available to get this right.
Also, if you have further questions, please feel free to upload a picture here.
The main thing, though, is that fenders almost always need a little nudging after installation to make sure that they are clear of both the tire and the V brakes if present.
I hope this helps. If not, please let me know what other questions you may have and we will get it fixed.
The fenders in the images below are very typical examples of how a fender might be positioned out of the box or upon installation. These fenders simply need to be moved in the desired direction by gently shoving or even thumping with the palm of the hand.
We are always happy to send out new parts, but in this case, new fenders will like'y need the same treatment.
You can refer to these Videos:
Please help our co-pedalers by voting if this article is helpful or not.