Hi,
There is a "RESET" button/ tab on the Sound page, just under Tune/ Map. That will reset the selected/ current slot.
Yes this will reset all the parameters of the selected slot.
I don't think there is a init/ default preset. But you can just create one or more yourself.
The kind of "init"preset is "Sarrar", only one slot is used, we didn't make a real blank preset because of the beginners that may take it for a bug.
Otherwise, as said LBH, you can reset all the slots then save it as an "Init" preset.