1) Find the highest point of the floor.
2) place a laser auto leveler on that point to give you a laser level line on the walls
3) etch the line on the wall with a pencil and a straight edge
4) use a sharp chisel and a 4lb hammer to chip holes into the low laying concrete, this will allow the new concrete a stronger bond
5) mix a skim slurry of 1 part cement and two parts of fine plaster sand
6) ensure that the area to be repaired is scrubbed clean of any oil
7) apply the slurry with a plaster float
8) once done, wait for 30 min and use a longer straight edge to screed the whole surface.
9) you may float - optional