Not sure about the part where Google resets index, but you can just redirect every request to a subdomain, if you use apache:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^example.com [NC,OR]
RewriteCond %{HTTP_HOST} ^www.example.com [NC]
RewriteRule ^(.*)$ https://ww1.example.net/$1 [L,R=301,NC]