Btukfyl

source

By restating these rumors, it’s they who are guiding the public
opinion, trying to influence people’s voting.

I think it's not a decent English.

马化腾 There are numerous grammatical and idiomatic errors in the linked article. It was clearly written by a non-native English speaker. I can't tell you if this is because it is a translation from the Chinese or for some other reason.

However, this particular sentence is fine. This use of "it" is what is called an "existential" or "dummy" pronoun, and is quite common. Other examples:

A: Thank you for making dinner for us!

B: You're welcome, but I can't take credit. It is my brother who did all the cooking.

It is true that I own a zebra.

Isn't it obvious? It is Professor Plum who committed the murder, in the library, with the lead pipe!

There's nothing wrong with that sentence. "By" here uses this definition of the word:

[often with verbal noun] Indicating the means of achieving something.

‘malaria can be controlled by attacking the parasite’
_{Oxford Dictionaries}

For this specific definition of "by", it is OK for the entire prepositional phrase to be moved to the beginning of the sentence.

Here's an example:

By doing that you made the whole crime worthless.
_{Cast in Order of Disappearance}

For hundreds (even thousands) of examples you can search . by *ing (the . matches a period and *ing matches words ending in "ing") in COCA (for American English) or BNC (for British English).