Hey @Sarath_CM,
I guess you are looking for something like this:
await strapi.db.query("admin::role").create({
name: "Super Admin",
code: "strapi-super-admin",
description:
"Super Admins can access and manage all features and settings.",
});
After that just edit the roles-array of your admin-user (“admin::user”). 
If you’ve trouble adapting that maybe have a look into my strapi-plugin to easily create a default admin on startup of strapi: