By default Helix 3 mega menu is adjust to off-canva in a screen resolution below 480px. If you want to have off-canvas menu for a bigger screen resolution just add below CSS code to your custom css file.

@media (max-width: 1200px){
.sp-megamenu-parent {
display: none !important;
}
#offcanvas-toggler {
display: inline-block !important;
}
}

Change '1200px' to whatever size you want.