And that method can be shared?
Yes, can be shared,
with a grain of salt (I haven't tried it again since a few years ago). I call it "defibrillator method", as in
let it die, then resurrect it.
Once again, this method of mine is useful for an older domain with very good backlinks, but for some reason doesn't rank well anymore. Likely due to stale content, thin content or whatever like that has brought it in the black hole. Here's what I did.
Step1. Putting all pages on 404 and letting G de-index for a while (say 1-2 months). Then deleting the domain completely, no DNS, nothing (keeping it registered though). The goal here is to completely de-index the domain and make clear to G the domain does not "exist" during this time.
Step2. Wait some time. I have typically waited for about 1 year.
Step3. Relaunch the site, with fresh content (not the same as it was). Can be in a different, but close related niche. Keep building content steadily for some time. Bring a few new links as well, from sites related to the niche.
From this point, you will most likely enter sandbox. In my case, sandbox was always the same: 3 months. The trick is to keep posting content, and do not be deterred by the sandbox. You will rank, but in the 10's or 100's.
Once it gets past that time (say 3 months), woosh - you'll see it suddenly in top of SERPs, and ranking again great like in the ol' times.
From this point on the cycle resets and you can enjoy again a few years of steady growth, if you continue to build it and update pages at least once at 3 months. BTW it is better to keep updated rather than always adding new content, and discarding pages that do not generate traffic.
Happy resurrecting.
Edit: It's not necessarily sandbox, but G algo being circumspect about your site for a while, and that you can count on.