How to optimize Old Paper Theme for mobile

Hi support team,

Our website is appswithoutcoding.com, and we are currently using the Old Paper Wordpress theme.

When our website is accessed via mobile, a strange button appears between the logo and the text, as seen in the first image.

When this button is pressed on, an "undefined" area shows up, as seen in the second picture attached.

How do we get rid of the button and the strange "undefined" space?

Thanks in advance,
Tushar and Andrew