Ghost followers in 2020

Long story short, I have a client who used some shady growth services before and they blasted the account with around 4k fake followers. The worst kind of fake followers. Now my client wants to get rid of all those accounts. I never did that before so I’m asking for your help.

Did anybody have any experience with this? Does it do any harm? Does it do any good?

Thank you.

I read before on some thread that you should never have decrease in followers because it will register your acc as bas one because you are losing followers.
If you tend to remove them, be sure to gain daily more than you remove.
If you want to remove 100, gain at least 115-120..daily growth of 20..have some space left for natural unfollow...
Hope it helps

I've read something similar and it stuck with me.
I don't think it will count as unfollows from people, I don't think IG it's that dumb.

But still, I never did that before so I'm afraid I'm going to cause some harm to the account.

I'm sure someone here did that before and it's kind enough to share the results with us.