Reverse changes

Is it posible to deleta a change?
I’m have tried to help a friend to reverse a change he made, but we only did it worse.

Hi and welcome to OSM and the forum

With every change on an OSM object (node, way, relation) the object gets a new version-number. A revert or rollback can be done by downloading the previous version of the object(s), replacing the values and upload the object(s) again (as a new version).

Can you post a link to the changeset(s) so we can take a look? ( → Your friends profile → My changes)