Prevent indexing subdomain

Hi,

I have a domain that is my main website and I’ll use domain.com here as example. I’ve just added a subdomain for testing WordPress websites so it’s staging.domain.com. In the subdomain I’ve only installed WordPress and configured multisite. But I can create sites in their own folders like this staging.domain.com/site1, staging.domain.com/site2 etc.. Everything is a fresh install with no sites in the subdomain folder until I get the no index set first.

The domain and subdomain are in their own separate folders in the root public_html.

Does anyone have a suggestions on how to prevent everything in the subdomain folder to be indexed? But still keep the main domain indexed. I’m not familiar with the right or best way to proceed because I don’t want to prevent my main domain to also not get indexed. I’m not sure if I should add a “<meta name=”robots” content=”noindex”/>”, edit the robots.txt or htacess file.

I could use some help if anyone knows how to. Thank you!