Same here. My home-button flex cable extended under the main board rear cover plate, and would have required removing screws to extract. So I left the original home button installed, and removed the one that came with the new assembly.
The ‘reverse order’ step are misleading. It is not trivial to reconnect the main screen flex cable to the main assembly — lots of trial and error to get it snugly plugged into the receiving connector. That part is glossed over. (Dissassembly is trivial. Reassembly is hard.)
After putting the screen and connectors on, I learned that there’s some plastic edging on the BACK. I had to remove the screen since it effectively wraps the home-button key. The new screen cracked. Great.