Can anyone inform me how to record a video call on my Tab 3?
To be able to record video calls on the Tab 3 device, you will have to install a third party application that deals with screen recording. Luckily, there are plenty applications available for this procedure. There is one app from this category that I have previously used and it's called simply REC. You can download it from the link attached below.
Download page: https://play.google.com/store/apps/details?id=com.spectrl.rec