On the Android version of the Meta Trader 4 or 5, you will be asked to enter the broker on the login page.
The broker is the login server of your MT4/5 and you simply have to enter "VTmarkets" and choose the server of your MT4/5.
The login server of your MT4/5 information could be found on the login credential email that has been sent to your email or on the MT4/5 list on the live account tab at the Client Portal.