I would like to add unique filters to users list of RainLab User plugin. How can I do that?

You might be able to achieve this by extending the users plugin. Check this resource for info about extending plugins.

Thank you for your answer! Unfortunately the video doesn't contain that, how to modify the config_list.yaml file or add filters to list.

look into the config_filter.yaml file configuration in order to setup some filtering in your backend controller list.