Hello @ddostech,
Thank you for reaching out,
Please share a live URL of your site page so we can inspect it.
If you are using a custom header, that header probably won’t follow the theme settings and should be checked within that same custom header. For example, if you’re using Elementor, you need to check the widget settings.
If it’s not a custom header, or if changes have been made in some way through the existing theme’s settings, you can go to WP Dashboard > Appearance > Customizer > Header > Mobile Menu > Breakpoints and adjust this option according to your needs. For example 480px: https://postimg.cc/VS7TJkf6.
Here is the related article about header menu in OceanWP theme:
https://docs.oceanwp.org/article/901-customizer-header.
Please recheck your issue and keep us posted.
I hope it helps,
Best Regards