Before import demo content Eidmart registration is required using your Envato purchase key. Please check this article to register Eidamrt https://doc.wpninjadevs.com/docs/eidmart/installation/eidmart-registration/
Within your WordPress Dashboard, navigate to Appearance > Import Demo Data.
Eidmart supports one-click demo import. You can install the marketplace demo within a click. Simply select the demo that which demo you would like to install then click. Please check the below screenshot-