Leveling concrete for bathroom installation
I'd just use more thinset in this area for the tile floor.  10&quot; isn't a huge area, 3/8&quot; height isn't a huge height difference and assuming you start tiling somewhere else you'll need this extra thickness for the tile to sit level with the surrounding tiles.
You could use SLC first on that one area but it just adds another step for little value.  If you were to add an extra step I'd probably just use thinset to pull this area up first.  Most SLC needs a primer and you'd have to buy at minimum a bag so unless you have some other uses for the remainder easier to go with thinset.