ultracrepidate
to venture beyond one's competence or purview
The new editor has a lot to learn and should be anxious not to ultracrepidate.
Where it comes from
From the Latin phrase ultra crepidam ("beyond the sandal"). An allusion to the response of the Greek painter Apelles to a cobbler's criticism, as recorded by Pliny the Elder.
Adapted from the Wiktionary entry ultracrepidate (CC BY-SA 4.0).