You can import either all listings or listings of a specific agent. If you need also to import agents profiles, you can follow the instructions here.
1. Make sure you've made filterable the field with Agent ID. Please note that this field can be named differently on your MLS provider side.
2. Then go to create a schedule and enter your Agent ID into this filterable field.
If your agent ID is correct and there are listings assigned to this agent, you'll have some search output.