Garage floor slab not in water - sanding

Good day everyone,

I had someone do my floor slab, it slopes down by 4 cm over 7 m (I know, it shouldn’t happen).
In order to properly install the sectional door, I obviously need a level surface.
The floor slab was afterwards surface sealed, that is, smoothed with a round disc and is quite smooth.

With which tool can I grind down 4 cm?
Thank you very much.

If there is steel in the floor slab, the 4cm less at the appropriate place will result in the necessary cover being missing. Really 4cm? Apparently, not only water flowed during the production of the floor slab o_O Then grinding is probably no longer possible. Heavy equipment is needed, meaning chiseling, milling, or similar. Is there alternatively the possibility to compensate for the unevenness of the floor slab upwards? (filling up)

Hello, thank you very much! Leveling the floor slab upwards would theoretically be possible, but the smoothed surface would have to be ground down and leveled with screed concrete, right? Thank you.

It only has to be leveled in the area of the gate, i.e. 10 cm wide. Then with the angle grinder. However, there are leveling compounds that adhere to everything and also compensate for 4 cm, but they are not cheap.

I had someone make my base slab, it now slopes down by 4 cm over 7 m (I know, it shouldn't happen). To properly install the sectional door, I of course need a level surface.

If the floor slopes towards the door, that's not a bug, but a feature!

If the ground slopes towards the gate, that's not a bug, but a feature!

But not like the OP describes it. (Not towards the gate, but along the length of the gate.) However, not everyone usually has a 7 m wide garage.