Click on Data --> Contacts --> All Contacts --> Lists --> Click on Normal/SuppressList
(Enter the details in the Create New List dialogue box and Click Create List)
Once the List is created mouse-hover the created list and use via File Upload method to upload the data in the panel.
The database that you upload should mandatorily have the 1st column as the primary key header. Apart from it, you can mention whichever Header you want, but make a note that the same should be already created in your panel.
You can refer to the below links for the same:
https://docs.netcoresmartech.com/docs/test1#video
https://www.youtube.com/watch?v=zTjMRH0W2y8&t=12s