To form the passé composé with the verb "être," you need to use the auxiliary verb "être" and the past participle of the main verb.
If you are looking to complete the sentence "je / être," the correct response would be:
"j'ai été"
This translates to "I have been."
If you are specifically looking for "être," as in the infinitive or you mean the auxiliary verb itself as part of a different sentence structure, please provide more context, and I can assist further!