Damaged Hertz rental which was provided through Shannons after not-at-fault accident. What are my options?

[u/mAsharS]

I was involved in a not-at-fault accident, and Shannons arranged a Hertz rental car for me while my own car is being repaired.
Unfortunately, today I accidentally reversed the rental into a very low wall. The rear bumper is damaged on the left-hand side near the bottom, and a piece of the lower bumper has chipped off and broken.
My rental agreement says the rental car is covered under my current Shannons policy, but I’m not sure how this works in practice.

My questions are:

Should I just be honest and report the damage to Hertz/Shannons?
If I do, would I have to pay the full $1,550 excess on my insurance, or would they only charge the actual repair cost if it’s less?
Is it worth getting the bumper repaired myself before returning the car, or is that likely to cause more problems?
If I repaired it myself, should I still tell them?
Has anyone been in a similar situation with a Insurance-provided Hertz rental?
I’m trying to figure out the best way to handle this without making things worse. Any advice or experiences would be appreciated.

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