Once the Ubigi account is created, you can top-up or purchase additional data top-ups at any time by connecting to your account:
-from the application:
Download it from the AppStore or PlayStore
Open a browser and go to ubigi.me, enter your credentials to access the account, then click on the TOP-UP tab.
If you forgot your login and/or password for your Ubigi account, refer to: I forgot my password, how can I reset it?