[Help] I’ve been attempting to install High Sierra on my computer to use checkra1n and I’m not sure how to boot into it. Help would be appreciated.

I begun with following a YouTube video on how to install High Sierra onto my Windows 10 Lenovo computer when I came across the issue. In the video (posted link below) he uses an older HP laptop to boot into the usb, but I’m not exactly sure on how to do that on my system. When I try to place my computer in recovery mode and boot into the usb, it says that security doesn’t allow for this. Could I get some assistance, please? Thanks.

Video