Gentlemen have an issue with ESXi interface, not a VSphere interface, I guess you all should know the difference by now, 
Indeed vSphere gives you an option to get Certificate to update your root CA storage on win or Linux, from where ever you are opening your web GUI
But this option is Not in ESXi GUI interface 
I'd suggest reinstall SSL by installing some cheap trusted root cert
by following VMware manual (Which is never 1,2,3,4 unfortunately)
Regards