There are various interesting points while responding to this question. On the off chance that the section has sunk a significant amount, then, at that point, you might need to consider having it raised before having it coated. The process involves boring openings in the concrete where it needs to be raised. Either a form of mud or foam can be pumped into the holes and underneath the concrete to lift it back into place. We do not specialize in this service so you will need to find a company that does it.
Assuming the floor is pooling water in regions, this turns into somewhat precarious. It is not that common to have a slab poured and finished perfectly level. There are self-leveling products that exist but, from our experience, when you level one area it forces the water to another area and you may discover a similar problem in another area of the floor.
The other issue is when you begin to lay product on top of other products, manufacturers get pretty picky with warranting floors because there is a higher chance of delamination. In general, it’s not recommended to try and fill in areas that are pooling. We do find that some pooling may be reduced when we coat the garage because we grind the surface of the concrete and coat it with self leveling products which tend to find their way into lower spots. It’s not a guaranteed fix but it may naturally help with the lower spots.