。
He said he'd come back here tomorrow.
Literal
Tomorrow here [to-へ] return-come [quotative-と] he [topic-は] said.
戻ってくる = 'return-come' = 'come back.' The ~てくる auxiliary here is compositional: 戻る ('return') + くる ('come') = 'come back (toward speaker).' The と marks the preceding clause as reported speech. Typical indirect-speech sentence.