Who is the manufacturer of the computer? I expect you did not get a manual with it but you should be able to go online if you have a computer which can do that and search for the manual for that specific machine. Do you remember how you accessed the BIOS initially to change the boot order to boot the USB? Does that method no longer work? What happens when you try it?

You have been asked if you can boot the installed Ubuntu or if you are using a USB with Ubuntu but have not answered that question. Which is it? You also indicated you made some change in boot to enable/disable something. Was this in the Ubuntu Grub or in your system BIOS firmware? You should always make notes of changes, particularly to system files and keep them written or on another device.

What exactly happens or what error messages do you get when you try? More specific information is needed.

If you can't download the boot repair iso and if you are still able to boot the installed Ubuntu or the Ubuntu usb and get online, go to the boot repair site below and use the 2nd option described on that page to get boot repair and run it by selecting the Create BootInfo Summary option only. Do not try to make repairs and post the link you get here. The PPA version is more up to date than the iso.

https://help.ubuntu.com/community/Boot-Repair

That was the only output of blkid?

at the grub menu press e for edit, What is the "set root= " line and the uuid number at the end of the "search --no floppy line ....."
At the grub menu press c, what is output of
grub>ls

Did you try one of the other grub advance options menu items?

It is fixed.

In my case, my PC is recent, and it has a button to press on it in order to restart the BIOS, similar to the router of WIFI.