Repasser can be used with avoir or être in compound tenses depending on its meaning in French (Le Passé Composé)

Most verbs use either avoir or être as the auxiliary verb in Le Passé Composé (Indicatif) (or other compound tense), but repasser uses both, depending on its grammatical usage* and what it means in the sentence.
 
*Grammaphile's Corner : the technical grammatical distinction between these cases is actually whether the verb is used in a transitive or intransitive manner. 
- The transitive version (the version with a direct object) uses avoir.
- The intransitive version (lacking a direct object), uses être.

Using avoir or être with the verb REPASSER in Le Passé Composé (Indicatif) in French

être + repassé [par, chez, etc]
= to pass by [somewhere] again
= to come back by [somewhere]
= to pop back in [somewhere]

Tu es repassé à la boulangerie car tu avais oublié les croissants.You went back to the bakery because you had forgotten the croissants.

Il est repassé par chez toi mais tu étais déjà parti.He came back by your house but you had left already.

Nous sommes repassés par le lac: c'était magnifique.We passed by the lake again: it was beautiful.

Note that in each case where être is the auxilliary, the verb repasser is followed by a preposition (en, sur, dans, à etc.).  
So in these cases repasser is usually about passing by again, coming back by somewhere, or popping back in somewhere

(See also Agreeing past participle with subject's gender and number with (+ être) verbs in the compound past in French (Le Passé Composé))

avoir + repassé [quelque chose]
= to iron [something]
= to retake [a test or exam]

Chéri, tu as repassé ma chemise pour demain?Honey, have you ironed my shirt for tomorrow?

Il a repassé tous les draps que j'avais laissés.He ironed all the sheets that I had left.

Nous avons repassé notre bac.We retook our A levels.

When repasser is followed immediately by a noun (as opposed to a preposition), it uses avoir as the auxiliary, like most verbs.
 
Here is the list of all "two-auxiliaryverbs in compound tenses:
 

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Examples and resources

Nous avons repassé notre bac.We retook our A levels.
Nous sommes repassés par le lac: c'était magnifique.We passed by the lake again: it was beautiful.
Il est repassé par chez toi mais tu étais déjà parti.He came back by your house but you had left already.
Tu es repassé à la boulangerie car tu avais oublié les croissants.You went back to the bakery because you had forgotten the croissants.
Chéri, tu as repassé ma chemise pour demain?Honey, have you ironed my shirt for tomorrow?
Il a repassé tous les draps que j'avais laissés.He ironed all the sheets that I had left.
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