You can’t:

It’s also important to understand the difference between databases and spreadsheets. While Airtable’s default grid view looks almost identical to a spreadsheet, databases and spreadsheets are structurally very different. What you’re calling a spreadsheet is a base in Airtable, and as @Elias_Gomez_Sainz pointed out, connecting bases is currently not an option. To help clarify some of the other key differences between spreadsheets and databases, I recommend reviewing this page in Airtable support: