Hi Floyd,
Indeed, if a user opens or closes the navigation by manually clicking on the hamburger button, the status will be saved for their session and the navbar will stay opened or closed, depending on their preference.
Note that you can set the default state in “Customizer > Appearance > Navigation > Layout” by checking the “Vertical Navigation Default State” field.
In case you want to edit this cookie, I’m afraid this feature requires custom development work. Please be aware that customization work is not part of the support we provide. In consequence, our recommendation is to hire a developer to do this job for you.
If you’re on a tight budget, we recommend you to require the services from Fiverr. This web platform gives you access to developers who already have experience with theme customizations, and for very competitive prices.
Disclaimer : we have no affiliation with Fiverr and are only recommending it as a starting point and a popular option for those who might not be sure where to look when in need of some custom work.
Best,