Sram etap AXS users - tech help

[Babw]

I got a new bike yesterday and like a wally without reading a manual I decided to try to adjust my lever reach but actually ended up losing a few drops of hydraulic fluid.

What does this screw actually do? Is it there to empty the master cylinder in the lever? It's on the inside of the shifter.

The lever feels a bit spongy so needs a bleed but I'd rather know if I've loosened something internally before I go and bleed it.

The shifter is a Sram Red AXS.