boot – Acer Aspire (No Bootable Device after installing ubuntu)

I bought an older version of Acer aspire es1-131 to run Linux on it,
I used the Ubuntu 20.04.4 LTS version and booted it from a USB (used Rufus)
it booted to the USB and allowed me to install it.
after installation is finished and restarted.
I got the big screen (No Bootable Device)
I installed it on the inner drive
and I did it twice one with the internet to install updates while installing.

I saw the question here
and followed the first answer but
couldn’t really understand part 5

5. In same folder, make sure UUID in *.cfg is referring where your ubuntu partition is.

so I skipped it and now my device is restarting infinitely
any help