I have been playing around with old hdds after discovering hdd enclosures. I hooked up a couple of them from older systems and installed other distros to play around. Anyway, long story short, my Grub got out of control and at one point, my grub was on one of the hdds in an enclosure, so I had to have it plugged in to my USB to get to my main UM.
Never having messed with grub, I soon learned about the grub file, updating grub, etc. I found myself making more of a mess each time I messed with it. I tried Grub Customizer but it made little sense and then I tried editing the grub.cfg file directly and I had some limited success.
Without getting into all the details, I FINALLY discovered this wonderful little link Boot Repair.
10 minutes after installing and running this little bad boy, I had my Grub back where I wanted it.
So if you are having problems with Grub and like me, you feel it’s a little over your head, give this a try.