If you have an original Kobo H2O, this is the procedure for a normal hardware reset:
https://www.kobo.com/help/en-US/arti...-kobo-aura-h2o
If you have a Kobo H2O Edition 2, the procedure for a factory reset is described here:
https://www.kobo.com/help/en-US/arti...-h2o-edition-2