"..does not contain a valid set of GRASS 7 modules.", how to fix?

Using 3.10.8-A Coruña, installation with GRASS tools.

I am trying to run Grass’ r.water.outlet tool and getting this error:

This algorithm cannot be run :-( 
The specified GRASS 7 folder "C:PROGRA~1QGIS3~1.10binbin" does not contain
a valid set of GRASS 7 modules. Please, go to the Processing settings dialog, 
and check that the GRASS 7 folder is correctly configured

It is not clear how to correctly configure the Grass 7 folder. My installation only has a GRASS 78 folder. I have tried the fix Micha explains here:

GRASS not working with QGIS 3.7

I go to Settings > Options > Advanced > Processing > configuration
The instructions say to go to the GRASS7 folder but my installation does not have a folder, it has GRASS7 log commands, log console, use vexternal and help; non of these allow me to edit the file path, apart from the Grass_help_path.

Can someone update this help for this 3.10.8-A Coruña version of QGIS please?