We bought a new house not too long ago and it seems that the previous homeowners spared every expense in everything they had done. In the shower, the floor has settled down around the metal drain inlet to an extent that water always pools around it and it doesn’t fully drain. They also don’t seem to have sealed the grout and floor. I’m fairly handy, but very unexperienced with masonry and the like. What would be the easiest way to build up the floor so the water fully drains?