Lookup fields in Airtable are different from lookup fields in a spreadsheet.
In Airtable, lookup fields are based on a linked record field. The lookup field shows the field in the other table only for the records in the linked record field.
Here are the main ways of getting a record into a linked record field:
- manually adding the record to the linked record field (either one at a time or in bulk via copy/paste)
- getting the "backlink" filled in when a link is created (this happens automatically for linked record fields between two different tables)
- having an automation that updates the linked record field, often with the results of a "find records" action
- using a script
- from an external source that uses the web API, such as a portal
It isn't quite clear what you want, but you might be able to leverage the backlink field of your existing linked record field to get the information you want.