Revive responsive banner not shrinking on mobile phone

Hi
I have just set up a website and everything is fine, except for the banner. It is not shrinking (being responsive) on mobile phone, or mini ipad; each side of the banner is cut off, therefore not shrinking to fit. The rest of the site seems to be fine.

Website address: https://gigised.com

Any ideas on how I can fix this please?

Many thanks.