「だ」 does NOT mean "to be". It is an ending for noun clauses; it is not a verb.
In this case, 「だった」 stands for an unspecified clause (most likely something someone else just said) conjugated to the past tense for the purpose of adding 「ら」. Thus, 「だったら」 means something like, "In that case,..."
「だ」 does NOT mean "to be". It
「だ」 does NOT mean "to be". It is an ending for noun clauses; it is not a verb.
In this case, 「だった」 stands for an unspecified clause (most likely something someone else just said) conjugated to the past tense for the purpose of adding 「ら」. Thus, 「だったら」 means something like, "In that case,..."