Do you really need a formula? Try using replace (Ctrl+H)--in Find what type
a comma (,) and in Replace with type an underscore (_).

"BorisS" wrote:

how do I write in a substitution of a comma? SUBSTITUTE does not seem to
like it when I just type SUBSTITUTE(reference, ",","_"). I need it
substituted with an underscore.

Thanks.
--
Boris