You will need to drill out the OEM rivnuts so you can install the reinforcement plate that comes with the amp steps, then install the new rivnuts. But it sounds like since you bought them used you probably do not have the plates or new rivnuts?
With that said I did not do that, I just used the existing OEM rivnuts and did not install the reinforcement plates. But I'm not a heavy guy so I wasn't too worried about it. Pretty much no one over 180bs ever steps on mine. If you have some larger/heavier people you expect to be stepping on them I would get those plates in for sure.
So far I've had no issues but proceed at your own risk if you do not put the plates in
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