When you import your leads manually to your campaign, you can import only the name and email address of your leads and you can not add additional variables for these leads, only edit the name and email address.
If you want to have more variables, you should import your leads via CSV file or Google Sheets.
To learn more about bulk import, read this article: https://help.instantly.ai/en/articles/6254215-how-to-upload-leads-with-a-csv-file