How do I resize the screen when using Viber on my Q10?

Hello! I have got BB Q10 phone and I just downloaded Viber version 2.3.5.329 it working fine the only probleme am experiencing is, i cannot take incoming call because the screen is too big just can't take the call. What should I do?
The screen is too large when receiving incoming call. Where i suppose to press getting calls is not showing on the screen. What should I do? Is there another Viber version i should download or what causes that?

Swipe from top and change the 'Size' (option on the RHS) to 'Rectangular - suitable for games'.

Assuming you have an up to date OS

PassportSQW100-1/10.3.1.2480 O2 UK