Hello @jcolacino the previous replies will be the easiest way to work with this .stp to trim the size quickly.
It would also be easy to just re-model from scratch. See attached.
You can drive the length of the pattern depending on how long.

Not sure what the end game is but I always find reverse modeling suppliers parts and converting to parametric models helps in the long run.
Another idea to think about, depending on the complexity of your part, you can use the Feature Recognition add-in to auto-generate known Inventor features.
App Store: Feature Recognition
I ran it on your part over lunch and it took quite a while due to the repetitive cuts but was successful. See attached.
For simpler parts it might be helpful, but in this situation it was a pretty terrible idea. Not really meant for patterns and came in with 71 Work Planes, 144 Chamfers, and 201 Extrusions, which isn't useful. I just wanted to see if it would work and what it would come up with.
Created in 2018 without asking your version so hope you can open them. Nice Hoover Dam pic, love that place!
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