Change menu breakpoint

My menu appear on bigger tablets (ipad pro 12.9″) as the desktop menu and it’s all jammed up.

I would like to change the breakpoint that is 600px to something bigger.
I’ve looked through the css but couldn’t find the specific code to change.

From the inspect tool in chrome I can see that when I cross the 600px a “flex” appears. Is there somewhere I can change this?

Thanks

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