Hi,

You can only put the image as the background. You can't change the input type submit to the image.

Regards,
PenciDesign.

Hi,

1. Please go to Appearance → Customize → Custom CSS then add the following custom CSS code:

@media only screen and (max-width: 767px) {
    #logo {
        padding-left: 0;
    }
    #navigation .button-menu-mobile {
        display: none;
    }
    #navigation .menu {
        display: inline-block !important;
        float: right;
    }
    #navigation.header-6 .menu {
        float: right;
    }
    #navigation.header-6 .pcheader-icon > a {
        height: 80px;
        line-height: 80px;
    }
    #navigation.menu-item-padding ul.menu > li > a {
        padding: 0 5px;
        font-size: 12px;
    }
}

#respond #submit {
    background-image: url('your-image-link-here');
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}

Regards,
PenciDesign.