Create a Custom Data field that matches the Custom value in the sheet that you would like to Upload.

In this example, the created custom data field is 'Address'.

Navigate to https://app.tallbob.com/contacts

Click "Drop file here or click to upload"

Select the file that has the Custom Data that needs to be uploaded and click "Upload" Button

Select a contact that has been uploaded and click on 'Edit Contact' and navigate to the extra fields toggle to find your uploaded custom data

Uploading contacts with Custom Data