No one can answer your question properly until we know the media container, codec, plus the horizontal & vertical dimensions of the file(s) you must DELIVER.
It's always about the delivery specifications. You work backwards from there in your AE project planning.
Knowing the nature of your 2.35:1 footage will also be helpful in judging what to do.
But to answer your question directly, and perhaps inaccurately, you can scale the footage to fit the comp from side-to-side. Highlight the layer and go Layer>Transform>Scale and you'll find it. Right next to it should appear the keyboard shortcut you can remember for future use.