How can an artist/bandman request to have their information deleted on MetaBrainz?
I do have a bandman friend and he doesn’t want his profile published on any website without any permision by anyone. Not even by me.
So what to do about that?
Is there any official email or contact for official deletion requests?
I see. So it’s sadly impossible.(thank you vkgy) 
Even to delete “wrong” birthplace is impossible?
If you know the birthplace is incorrect, you can put in an edit to remove it (empty the field on the editor form). Editors shouldn’t add back known incorrect information.
But then it should be proven that it is incorrect？
We generally trust the word of artists on their own data, at least where such personal details are concerned.
So if a fan once found it on the official twitter, but the official twitter has been deleted or the past tweets has been deleted, its enough trust to have it removed?
Per How does the EU General Data Protection Regulation (GDPR) affect MusicBrainz data - #5 by rob MusicBrainz could also remove birth month and birth date (but not birth year or birth place?).
Most of the time, editors add legal names, birthdates and places without sources, and then everyone just copies the unsourced information, regardless of whether the original data could be verified or not before it proliferated throughout user-edited websites. I would hope reasonable editors wouldn’t vote against removing data that has no source and low expectancy of accuracy (i.e., the removal of guessed Japanese name romanizations).
Voters are supposed to assume editors are acting in good faith (bar sustained malpractice).
according to the Data Removal Policy (linked above), if the artist wants their birth info removed, they can follow the steps in the first section