Hi Scott,
Please follow the below steps to upload files into Adobe Report builder library.
Step 01
Click the Library

Step 02
Click Browswe on the Pop up dialog box

Step 03
Choose the Excel file version

Step 04
Choose the required file and Give some name in the description field and click upload button.
When you upload it may throw an error to configure FTP so try again after 2 - 3 minutes.

Result

Hope this helps.
Regards,
Kumararaja K