Account Migration has not begun. There will be an in game message when it's your turn to move. Do not fall for any third party websites that are telling you to migrate NOW. They're trying to steal your information.
Apologies for that. You still have some time since account migrations have not begun. You’ll see a note in the launcher when it’s your turn. More info can be found at https://help.minecraft.net/hc/en-us/articles/360050865492-JAVA-Account-Migration-FAQ …. ^RL