To create a sub-account you need to click on the "Create sub-account" button
You need to create a unique account name, set a commission (or set 0% if you don't have one) and write a comment, if necessary - this will help you better navigate through the list of clients.
The sub-account will immediately appear in the client list and in the accounts switcher.
Once created, you have full access to the sub-account - you can change its wallet and minpay and set any commissions using 2fa from the main account.