美国采购需求：双杠哑铃、哑铃套装、健身哑铃、健身器材、健身房器材、氯丁橡胶铸铁哑铃

I recently received a stair stepper in black/gray, but I'm encountering an issue with assembly. Specifically, the second step has a hole that's partially covered, preventing me from fitting the locking knob properly. I've tried a few workarounds, but nothing seems to work. Could you please provide guidance or a solution for this problem? Any tips on how to resolve the issue or if there are replacement parts available would be greatly appreciated. Thanks!