Override is formed from the irregular verb ride.
The Principal Parts of ride are ride, rode, ridden.
That means the PPs of override are override, overrode, overridden.
With me so far?
OK, the first PP in each case is the Infinitive form (to ride, to override).
The second PP is the Past form (They rode it, They overrode it)
The third PP is the Perfect Passive Participle (They have ridden it, They have overridden it).
The Perfect Passive Participle is the verb form that one uses with be in the Passive construction, and -- as here -- with have in the Perfect construction. One does not use the Past Tense verb form with an auxiliary verb in any construction.
Executive Summary: *Was overrode, *has overrode, and *be overrode are all ungrammatical.