First of all, your GCS (PC program) version must match your firmware version. If Danny told you to download something then it may not match.
Unplug your board, go to the Firmware tab, press Rescue, plug the board in. Does this work and connect and tell you what version your bootloader is?
If it worked (and your bootloader version is V4), you should be able to just press UpgradeAndErase. During the erase portion, make sure to let it run for at least a minute or two. FlightTime should count up to say 120 before powering it off. If everything is working now, you are done.
Here is a link (to an off site link) on how to update your bootloader if it is V3 (it needs to be V4).
https://librepilot.atlassian.net/wiki/spaces/LPDOC/pages/5669026/Firmware+TabAlso, you might be able to use CleanFlight to flash ef_coptercontrol.hex if you would rather try that than the external link instructions.
Please post a link to the Danny's video so we can see if he does something wrong.