How do Add manually the balance from the main account to the sub-account?

You have to click on the Contact/Database tab from the left side.

Search for specific contact using Email or Phone Number.

Click on the specific contact to where you want to add the balance and update the balance.

Once you Click on contact you will see all details on right side as mentioned in below screenshot:

Click on update balance and add the amount which you would like to add for that specific sub-account.