how to assign one user to thousand of database simultaneously using mysql in phpmyadmin

hello, i'd bought the vps server special for this multi db wordpress project. can anyone in support team know about the script that can assign one user to thousand of database simultaneously using mysql in phpmyadmin. I'm lack of knowledge in mysql but little bit know about php and html. Can someone in support team help giving the mysql that easy to understand for me or list of example script?

example for adding mysql script:-
host= local host
database = data_1, data_2......,data_4092,
database user name = data_user
database user pass= pass123

need help please