Will Revert at the Earliest?

It means "Please wait and we will get back to you as soon as possible regarding your schedule". The use of "soonest" here sounds quite old-fashioned.

Will revert back to you at the earliest?

The word 'revert' itself means to return to a previous subject or condition, so the insertion of the word 'back' in the sentence is incorrect. The correct thing to say is: ~ "I will revert to you shortly."

Will revert soon meaning?

While revert means to return to something earlier or to go back, it's often used wrongly in combination. If you're buying the older version of the game, you might say you're "reverting back," which is like saying "go back back."