Replace the Liftgate Grommet on my estate octavia Mk4 instruction and advice.

I found both liftgate grommets broken on my Octavia and suspect them of causing small corrosion on the tailgate and a previous issue with the brake light (water got inside). I want to replace the grommets and assume I first need to remove the interior trim from the tailgate. Since I have zero experience with such work, I would appreciate some advice, or perhaps someone can share official instructions.

Thanks in advance.