Hi and welcome.
Remove kickplate trim alongside seat, move forwards to trim panel and remove. A 4" square hole is what you are after. If RHD and drivers side, unscrew and pull out the fuel cut-off square box below the hole as much as possible.
What a PITA this job was on a hot summers day. My replacement was a non-original part that looked a little smaller than OE, but it still took an hour or so, be patient keep trying. Aim to get the door fixing bracket in first, then aim that upwards, while getting main part through, before rotating door bracket rearwards towards door. I think thats what worked for me anyway. Always hated rubik cubes, this is the modern version! Good luck.
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