Do you have photoshop, if so it's really easy. In CS6 upwards, if you just use the magic wand tool or marquee tool to select the white area (on a flattened version) and press backspace, the fill dialogue box will appear. Use the content aware setting and it will fill it for you with a indentical pattern.

Please Help.
Thanks !

I didn't find the right solution from the internet.
References:
-https://forums.overclockers.co.uk/threads/can-someone-extend-a-background-for-me-in-photoshop-please.18789895/
- Mobile App Explainer Video Examples