In our demo application and environment, we not create screen workflow to manage bank users.
As admin you can login to WSO2 management console: https://api.lion.mlabs.dpc.hu:9443/carbon/ (Lion bank) or https://api.elephant.mlabs.dpc.hu:9443/carbon/ (Elephant bank).
Select "Add" at "Users and Roles"
Select "Add New User"
Fill the required datas and select "Next>" button.
You can change role assignment.
In our demo we not using any roles, keep "Internal/everyone" checked, and select "Finish" button.
TODO You must assign username with Fineract account at OpenBanking gateway