Email
Why not just download the user table as a csv and upload them as contacts to your email provider.
If this is something you need to do a few times a year then don’t over complicate it by spending time on building a process in Adalo.
If you really want a solution in your app
Choose an email provider and read their API docs and help files. Build this kind of form in the youtube vid, then you’ll have the skills to move ahead.
Push notifications
The problem with relying on push notifications is… only users who have given permission for them will receive the update notification.
Forced update
There is a method for forcing an app update.