ᐅ Assembling an IKEA FAKTUM corner base cabinet with a bottom panel

Hello everyone,
after having searched your forum anonymously a few times, I finally want to come forward today as a (critical) IKEA fan. Maybe someone can help me.
Here’s the situation: I bought a Faktum corner base cabinet 120cm (47 inches) to complement my kitchen setup. The carcass is already assembled, although the instructions were quite poor. But I’m not completely clueless and this isn’t my first time... Now I just need to install the shelf (RATIONELL, about 116cm (46 inches) long). Unfortunately, this shelf isn’t mentioned at all in the carcass manual, even though I believe it is essential. There are no instructions for the shelf itself.
The package includes:
- the shelf itself
- a steel sheet support, 116cm (46 inches) long
- 2 standard shelf supports
- several screws
- 2 white plastic pieces, whose purpose I cannot guess.
Could someone provide tips on how to install this? IKEA is far away and there are no instructions online either.
Many thanks from
DerHolle

P.S.: Never mind. After some trial and error, I found a solution I can live with.