Learn English – When and How to use *We are to* and *We have to* in Sentence

It's "Have you returned from the conference?".

Be can be a helping verb with the -ing form of the verb (to express progressive tenses), not the -ed form.

For example: "I am returning", "she was returning", etc.

So, in interrogative mood, it would be "Are you returning from the conference?".

If you want to ask a question, but don't want to use a progressive tense, and aren't using any other helping verbs like have, will, should, you'll generally need to use do as a helping verb.

Did you return from the conference?

These participle phrases can be added to a sentence to explain the reason for the main part of the sentence. I'd prefer the first example to be something like:

Having seen my mother work tirelessly, I was inspired to work hard.

In this case you can see that the subject of the sentence is "I".

OR the participle phrase can be the subject of a sentence. In this use it is sometimes called a gerund.

There is no need for these to use perfective (have+V3) you can have -ing verbs with no "have":

Eating the apple, I walked down the street.

Eating the apple helped me to think.

I am not keen on your "it" structure: I don't like "Eating the apple, it helped me to think". It's correct grammar, but the gerund pattern is more natural.