Bulk add existing WP subscribers

Hi there,
I was running the prior version & all my subscriber level users had access to protected content (it’s a private site, so members must register to gain access).
Since the upgrade non of these subscribers have access to the protected content.
I know I can add them to a membership group (one at a time) but I have 65 subscribers so would like to avoid that if possible.
Is there a way to bulk add those existing subscribers?
Or a setting somewhere that allows an existing WP user role to have access to that protected content?
Thanks in advance.
Jason

https://ww.wp.xz.cn/plugins/membership/