Just did this retrofit this morning for my August 2021 build Model Y after getting my part in . I wasn't planning on installing till the next update which I figure was coming soon, but once I got home, an update was waiting. I signed up for the free annual service manual at
Tesla Service and searched for ECU - CHARGE PORT and removed a few trim pieces and lowered down the seat. It was actually easier then I thought. Had plenty of room to work with if you take the time to remove the trim pieces and you're able to pull it back further. I think total time was 30 minutes with reassembly. I installed the update and now CCS ADAPTER ENABLED!