Can't use my account after mojang/microsoft sync

I played wynncraft around 2014-2016 and decided to download minecraft and try it out again. I had to sync my mojang account to a microsoft one, but after that it asked me what usernamem i would like to use and I couldn't use my old one (metusalem) because "it was taken". After choosing new nickname I couldn't access my old account in wynncraft so is there a way I can sync my new one with the old one?

 

Issues can occur if a) you have had restrictions on your Microsoft account or b) you have played Bedrock or used Minecraft via a different email.
A) can be fixed by having the administrator upgrade a kids account to an adult account
B) Creating a new Microsoft account with the email used for mojang