How did you do it!

[Silverobama]

Two years ago, I chatted with a guy online. At that time, he had only 100 followers but yesterday I took a look at his profile. To my surprise, he had 100,000 followers.

I was so surprised and curious to know how he got these followers. I asked:

How did you do it!

Is my question good?

 

[aga6]

Two years ago, I chatted with a guy online. At that time, he had only 100 followers but yesterday I took a look at his profile. To my surprise, he had 100,000 followers.

I was so surprised and curious to know how he got these followers. I asked:

How did you do it!

Is my question good?

Your question could be slightly improved. Here’s a refined version:

"How did you do it?"

Now, there is a chance to know, because it is a question.

To be more clear, you can ask:
"How did you manage to gain so many followers?"

This version maintains your curiosity and surprise while also clearly asking about the process or strategy the person used to achieve such a significant increase in followers. It's direct and straightforward, inviting the person to share their experience or methods.

 

[Silverobama]

Two years ago, I chatted with a guy online. At that time, he had only 100 followers but yesterday I took a look at his profile. To my surprise, he had 100,000 followers.

I was so surprised and curious to know how he got these followers. I asked:

How did you do it!

Is my question good?

Teachers. Could you please help me with this?

 

[Rover_KE]

It’s a question … what do we end a question with?

 

[Silverobama]

It’s a question … what do we end a question with?

I was about to write "How did you do it?!".

Is the question natural?

 

[emsr2d2]

If you want to express both the question and your surprise that the person managed to do it, then an interrobang (a question mark and an exclamation mark) is appropriate. Bear in mind that not all native speakers use it (or like it) and I certainly wouldn't use it in a formal situation like an exam.
If you look online, you'll see that it's meant to be written as if it were one symbol, with the two marks taking up just one character space. However, I've never found a way of doing that on a computer keyboard.