2016? Hopefully, you already fixed this.
Anyway, there are good videos on YouTube for changing the 70D focusing screen.
I liked this one: https://www.youtube.com/watch?v=emRvWkP5...
The process is easy, but delicate.
You should wear gloves.
You will need the replacement screen to be available, but safely out of the way so it does not get dirty or scratched.
A magnetized small phillips head or JIS screwdriver and good tweezers or forceps are needed.
You should use a clear, clean table space. You will need to remove screws, so it is best not to do this over carpeting or some flooring surface where a dropped screw can get lost.
It is best to have good lighting, and not much air motion from wind or fans.
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