From other's conversation,I found out they mentioned I was and sometimes they also mentioned I were. Is there any rules for I was/were?
Purdue OWL has this example which is almost identical to OP's case: One of the boxes is open. The verb agrees with the subject, "One". If you wanted to talk about "two", you would use a plural verb: Two of the successful managers were asked. One of the successful managers was asked.