Well,yeah I know how to flash bios but in the video he is updating bios on a working pc with a supported cpu... so,I either have to buy a motherboard that supports 9th gen out of the box or a different cpu...You can update your motherboard with a USB stick, without needing a CPU, download the file into a USB stick and update the bios.
Assuming you never done this before, you can followt his guide:
(use the files you need, not the one in the video as they are probably not the same)
Edit:
Listen to Darkbreeze haha, i need to update myself before saying too much
View: https://www.youtube.com/watch?v=SgTokymDCcs