Hi Sonja,
Here is a CSS you may try:
@media (min-width: 769px) and (max-width: 1024px) {
nav.main-navigation .inside-navigation.grid-container {
justify-content:center;
}
nav.main-navigation .inside-navigation.grid-container .navigation-branding {
margin-right:0;
margin-left:0;
}
}
Here is an article with regards to adding CSS: https://docs.generatepress.com/article/adding-css/#additional-css
Adding this through additional CSS should work.
Alternatively, you can also try setting the Mobile Menu Breakpoint to 1024px so that the menu turns in to a mobile menu on tablet as well. This would prevent it from going down.
Hope this helps! 🙂