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Potential re-grouting or putting more sillicone round 2 shower trays - both upstairs and sillicone in 3 bathrooms where the floor tiles and vanities meet

Bought a brand new house, builders won't come back and sort out the showers in 2 bathrooms. Both showers, where the trays and the tiles meet you can see the bottom of the tiles so I am "assuming" more grout is needed or maybe they need to be silliconed? In the bathrooms (3 and 1 toilet), where the vanities sit on the tiled floors they have not silliconed and water could potentially get under the vanity units. May be a small job or may be a bigger one if there is a problem with the shower trays dropping slightly?? Thanks