Check your users locations based on the IP saved on the last login on site. Ip-Api is the service used to check the location and no api key is required to use this service.
Please check the site for more information about the limitation for free usage of the API ip-api.com
This plugin will include a link in user table and a pop-up will display the info returned by the API like:
If you need to check a different IP, you can use the form available in the plugin page and see the information related with that ip.
No changes are needed, for this plugin to work, but make sure that you don't have any js errors on your site, those errors can affect the functionality of this plugin.