There's access into the engine bay behind the glove box
Peel back the carpet and you'll see it.
You just pull the sill trim up, carefully. Dead easy. I highly recommend buying replacement clips etc ahead of time because they always break or fly off somewhere. Such is the way with VW trims, they are designed to be fitted once. Once you pull them off, they never go back on the same when reusing the clips, so fit new ones regardless.
You'll need clips for the sill, B trims, rear door cards (if a 3 door) etc etc. All of it really!
Oh and get some plastic trim tools from Amazon / ebay, they're handy for interior panels.