I remember reading about this about a year ago, so I'm not sure what the source was and how reliable it was, but I found this meta-analysis of studies researching the effect of the vaccine on people who had previously already received treatment for HPV: https://pmc.ncbi.nlm.nih.gov/articles/PMC8879645/

This seems to indicate that the vaccine reduces the risk of finding abnormal cells and precancerous lesions for people who already have HPV.