Pest Control HELP: I hear an animal in my attic crawl space. Is there a DIY way to get the animal to leave the attic while....?

we search, find and repair the entry point of where this animal is entering? I am not quite sure how it would be possible for an animal to get into the attic other than the roof somewhere.
Update: This animal is larger than a mouse. I am thinking it's a squirrel.
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