Similar examples: To put it another way, ... = In other words. To tell you the true, ... / To be honest, ... = I'll be honest with you. To make long story short, ... = I'll give you the gist of it. To make matters worse, ... = This is/was the bad thing.

To begin your sentence with an infinitive creates an interesting grammatical structure. As others have pointed out, it is the same as if you started the sentence with "In order to..." But how does one explain it grammatically? Look back at the start of the first sentence in this paragraph that you are now reading: "To begin...infinitive". It is an adverbial clause. It uses the infinitive "to begin" as an adverb, which is possible because infinitives can act as nouns, adjectives, or adverbs. That adverbial clause modifies the verb of the sentence "creates" because it explains "how" "an interesting grammatical structure" is created.

To return to/answer/address/go back to/ your earlier question…. = With the purpose of returning to/answering/addressing/going back to/ your earlier question….

I agree with Eric. I most often hear REVERT meaning to go back to a previous version: After I upgraded to Windows 27, I realized that my system couldn't handle it so I reverted to Windows 26.

To answer your question... Using an infinitive like this is a way of indicating the purpose of what we are about to say. There is no explicit subject of "to revert." You can imagine a complete sentence like this: To revert to your previous question, [I will say]... You could think of the person speaking as the implied subject of a finite verb which is left unexpressed here. This is common enough to learn. Both the complete structure (e.g. To respond to what you've said, let me say...) and sort of "halves" like your example are often used. The structure with just the infinitive, like your example, is common in conversation. The full version sounds a bit more formal to me. Your example sounds quite odd, though. The verb "revert" is not, as far as I know, used this way (although I haven't seen the rest of the context). Hope that helps!