I just found a mark on a rental car that I have had for about a week and am unsure what to do.

Long story short my personal car got damaged and had to be repaired so in the meantime I have had a rental car. The other day I noticed some chipped paint on the back bumper that I had not noticed before. I honestly couldn’t say if it was there the whole time or not. I didn’t cause the mark but I am worried they will accuse me of damaging it and make a claim on my insurance (I have a $500 deductible). Should I just take it upon myself to have it fixed or just wait and see what happens?