additional filter icon on mobile phone

It looks like you already use a header icon widget or similar feature for your existing icons. Is this part of your theme or is it a plugin? All of the elements have class prefixes “wd-“, as in “wd-tools-element”. Typically the “wd” is the theme’s or plugin’s initials. For example many WooCommerce element class names start with “wc-”

Whatever this module is, I recommend asking through their dedicated support channel for how to add a filter icon. You might need to add it for both desktop and mobile views. The desktop version could use custom CSS to hide it there if you would prefer.