Hello,
if the bootloader gadget can't be found this means that erp5_officejs bt is missing. You can automatically install this bt an all needed for the tutorial by using the OFFICEJS SDK configurator.
Please go to the favorites menu on top left of your ERP5 instance -> Configure your Site -> OFFICEJS SDK Configure. Then follow the steps and wait for the installation. This should solve your issue.
Regards,
Roque