Joseph taught that Elijah returned the Kirtland Temple
“After this, Elias appeared, and committed the dispensation of the gospel of Abraham, saying that in us and our seed all generations after us should be blessed.” -Joseph Smith, D&C 110:12
Joseph Smith took Malach 4:5 -6 "Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse."
Jesus taught that John the Baptist was the prophetic fulfillment of Malachi
For all the prophets and the law prophesied until John. And if ye will receive it, this is Elias, which was for to come. He that hath ears to hear, let him hear. Matt 11:13-14
And his disciples asked him, saying, Why then say the scribes that Elias must first come? And Jesus answered and said unto them, Elias truly shall first come, and restore all things. But I say unto you, That Elias is come already, and they knew him not, but have done unto him whatsoever they listed. Likewise shall also the Son of man suffer of them. Then the disciples understood that he spake unto them of John the Baptist. Matt 17:10-13
And they asked him, saying, Why say the scribes that Elias must first come? And he answered and told them, Elias verily cometh first, and restoreth all things; and how it is written of the Son of man, that he must suffer many things, and be set at nought. But I say unto you, That Elias is indeed come, and they have done unto him whatsoever they listed, as it is written of him. Mark 9:11-13
But the angel said unto him, Fear not, Zacharias: for thy prayer is heard; and thy wife Elisabeth shall bear thee a son, and thou shalt call his name John. And thou shalt have joy and gladness; and many shall rejoice at his birth. For he shall be great in the sight of the Lord, and shall drink neither wine nor strong drink; and he shall be filled with the Holy Ghost, even from his mother's womb. And many of the children of Israel shall he turn to the Lord their God. And he shall go before him in the spirit and power of Elias, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just; to make ready a people prepared for the Lord. Luke 1:13-17