Free WP Move Users Wordpress Plugin allows you to quickly move users from one WordPress site to another. Its WordPress Multisite ready so the plugin even works on entire networks.
WP Move Users – WordPress Plugin Features
- Export Users: To export the users you have multiple options. You can export all users or choose to include or exclude specific users based on user IDs.
- Import Users: Once you exported the users on the first site you now can just paste the export code which will import the users into the new site. If your running a Multisite network you will have the option to add the users to a specific subsite, add them all to the main site or both to a subsite and to the main site.