How do I unlink minecraft acc if I don't know any of details?

I am trying to sign my son into minecraft account on ps4 &5, but it saying already signed in with a gamertag we don't recognise. I now know one of his friend's had set him up an account a while ago therefore I don't know any of the details! How do I unlink it so I can sign in with my details? Please help

Even if you could unlink the current Microsoft account you wont be able to link a different Microsoft account:

LINKING A MICROSOFT ACCOUNT TO A PLAYSTATION® ACCOUNT

Note: Once a Microsoft account has been linked to a PlayStation® account, neither the Microsoft account nor the PlayStation™ Network account can be associated with a different account. 

If you choose to unlink accounts, then purchases will be returned to the account which made the purchase. Even after unlinking, Microsoft and PlayStation® accounts can only be re-linked to the original account.

Source: https://help.minecraft.net/hc/en-us/articles/360037725571#h_01FANTJMTM2689F8H1VA2F559Y

Hello, first it's a pleasure to be able to help you today.

My name is Welcome to the community.

Hello Rhona, If your child's Minecraft account is really linked to a friend's account and you don't have access to the account, unfortunately only the owner of the account could request the unlink with support.

I am seriously not sure how to even unlink it. I accidentally did the wrong email completely. Now it won't let me undo it or even unlink that account. It is just saying " We tried to gin you into your Minecraft account, but something went wrong." And I
don't know what to do to fix it. Can someone tell me step by step how to get this undone?

My name is Fernando I'm an independent consultant, I'm happy to help

Unfortunately, as you do not know the name and e-mail, it would not be possible to access it in order to stop the incident, I recommend that you speak to your financial institution and report the incident.

Hope I helped and see you soon

none of it works I cant contact PS support and cant unlink my Microsoft account it wont even give me the option.

All I need to know is how to unlink my Microsoft account to my ps4 then I'm good, so can u please tell me how to do that. (cant do it in Minecraft settings, wont give the option)