Put the verb in brackets into the past perfect.
I couldn't find the address. (not/be) I to that town before.
We build the past perfect using the auxiliary verb "have" in the past tense and the past participle of the main verb:
had + past participle
Regular verbs form the past participle with the -ed ending — exactly like in the past simple.
play — played — played want — wanted — wanted finish — finished — finished