Hi there,
I’m guessing that you have a multisite installation of WordPress?
If so the only user role capable of managing subdomains or sub-sites is the ‘Super Admin’.
This however allows a user to change the site settings and themes as well, this could be a potential risk.
I would suggest creating a custom user role or upgrading a lower user role like ‘editor’.
You can easily achieve custom roles with the plugin ‘User Role Editor’ (https://nl.www.ads-software.com/plugins/user-role-editor/).
But only the pro version of this plugins allows for ‘Super Admin’ capabilities to be managed.
I hope this works for you.