Right now there isn't an option for letting users import CSV files from the live app. They would need to have access to the builder and you can only have a limited number of shared builders with access to the builder.
For now, some customers have given their users the ability to add data within another service and then automatically import that data into their Knack apps. For example, you could have users add data to a Google Sheet and then create an automation using Zapier or the API to import that data into your app. See Can I schedule or automate imports?.
To show your support for the option to have users import data from the live app, vote on this feature request: Live App Record Import. Your vote will increase the visibility of this issue on our product backlog. You can also follow the request to stay updated on any developments in this area.