Hello, @zeryabadrichem,
Actually, the search bar already appears on the mobile as you can see here: https://postimg.cc/94XY4nHZ But to get this in the center add the CSS code in the PORTO >> Theme Options >> Skins >> Custom CSS >> at the bottom of the black box.
@media(max-width:575px){
#header .searchform-popup .searchform{
margin-right:75px !important;
}
#header .mobile-toggle{
margin-right:250px !important;
}
}
After that save the settings and check back to your site the result will appear like this: https://postimg.cc/fk8VFf4J
Best Regards,
PThemes Team.