How can I sync more my other site user to main server?

How can I sync more my other site user to main server ?

If I have 10 domains ,

Test01.com ~ Test10.com
the main domain is Test01.com how can I ,Test02~Test10.com add or register new user , it can auto sync to my Test01.com ( main domain )

Hi Andy,

I am not sure that fully understand your requirement. Can you please send us more details?