The first major revelation Joseph Smith received was D&C 10, given two years before he started his church. Originally, the revelation read as follows:
20 And thus, if the people of this generation harden not their hearts, I will work a REFORMATION among them (Book of Commandments IV:5)
By the time of the 1835 printing of the Doctrine and Covenants, that sentence (and much more) was removed, but allowance for him to start a church was retroactively added—as if Our Lord misspoke (if He gave this one):
5 Verily, I say unto you, that woe shall come unto the inhabitants of the earth if they will not hearken unto my words; For hereafter you shall be ordained and go forth and deliver my words unto the children of men
14 And to none else will I grant this power, to receive this same testimony among this generation, in this the beginning of the rising up and the coming forth of my church out of the wilderness — clear as the moon, and fair as the sun, and terrible as an army with banners (D&C 5:14 compared with Book of Commandments IV:4; emphasized words were added later by Joseph).
Thus, the view that the Mormon Church is a “restoration” is a faulty premise; that’s not how it originally was.
How was this reformation to have been performed? By the truths in The Holy Book of Mormon, which contains the full and complete Gospel of Jesus Christ. So if it’s not in The Holy Book of Mormon, then it’s not required for your Christian salvation/Mormon exaltation. Where the Lord resides IS the highest level of Heaven.
2 In my Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you.
3 And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also. (John 14)
23 But if ye receive me in the world, then shall ye know me, and shall receive your exaltation; that where I am ye shall be also. (D&C 132)