How to rank subdomains fast?

My customers can create a help center/knowledge base for their businesses through my platform. The content is delivered through a subdomain that they pick at sign up.

I'm trying to rank these sub domains in google but I'm not sure what approach to take. Do I manually create an instance in google search console and submit a sitemap for every subdomain created? Is there any downside to this, ie would google penalize me in case my customer numbers grow?

Or is there a different, more automated way?