How do I use :UpdateAsync if I want to update a spezific value in a table?

The question is in the title, thanks for help.

well, you replace the old table by the new one or
you replace the old value in the table by the new one

Ok, but what do I need to write in the code to update one spezific value in the table?

something like this:

Table[OldValueKey] = NewValue
return Table