Use the customer's file to make a xlsx file in Generic Year format. (sample attached)
If not included, add two rows for stats Available Rooms and Retail Rooms.
The file name is in this format QBODFWBF2021Budget.xlsx and copied to the QBO\Budget\Buddy\Hist2021 folder.
Be in Forecast 2021 mode. Then switch mode to Budget 2021 (which is locked and stays locked). [The reason you do this is that accessing an Approved budget turns all the accounts to Manual and prevent formulas (e.g. payroll) from calculating.]
On the Main Menu in Buddy, there's an option 'Load Budget from Excel File'.
See canned response for file attachment