[mothered]

Should I contact them and make up an excuse to make it look like I found the item? I would like to just return the PS4 as this investigation won’t probably go in my favor.

If It were myself, I'd let the Investigation take It's course.

The worst that can happen, Is they'll decline your claim. If they don't, then your SE will succeed.

but do you think I can still return the item after the investigation?

You certainly can.

Make an excuse that your little brother took the Item without your knowledge, and you found It In his bedroom a few days later.