Dear Dexter @dexter
In the Customize section you have the option to 'center' however if this is not a solution for you there is:
margin: auto - left and right
https://www.w3schools.com/css/css_margin.asp
or using Calc: to keep things centre
https://www.w3schools.com/cssref/func_calc.asp
or if applicable align-items, but this requires 'flex'
https://www.w3schools.com/cssref/css3_pr_align-items.asp
There are a few ways - if you could post a link to your website with the menu in question and then we can see what suits! :)
Best wishes
Richard