change the network administrator – super admin

What are the procedures for changing the network administrator (Super Admin)? I have a small business, I am the owner and mentor, financial and all. I hired a developer to create my website. I payed the domain, I payed a theme of network (child). This person, when he installed the theme, automatically became the administrator of that network, ie is the Super Admin. Now, for reasons of force majeure, need to change this, pass this function for me because I need to have complete mastery over the site, since this person no longer works for me. Only he can do that? Is there any way for me to do this because we are struggling to contact?