if you can't boot up your OS then it means you (to my limited knowledge) have no access to # lsblk. So i think Wiz means he wants to to boot up a live OS and run that command from the live OS.
I've been reading up grub2 in readiness that at some point in the 12st Century Slackware will adopt Grub2, currently it uses lilo and elio.
Now the difference between grub rescue > and grub > is that in grub rescue, it can't find the .mods which your image confirms.
You can try and look using ls to locate .mod stuff.
If you are going to have to get a USB with a live OS then i would like to suggest you try ventoy 13 relesase which will allow you to save time but putting intact iso to boot up including :
│ ├── bionicpup64-8.0-uefi.iso
│ ├── rescatux-0.73.iso
│ ├── slackware64-current-install-dvd.iso
│ ├── super_grub2_disk_hybrid_2.04s1.iso
│ └── systemrescuecd-amd64-6.1.4.iso
the super_grub2_disk_hybrid_2.04s1.iso Obviously Slackware never fails (more humor Wiz) and i'm using uefi and elilo but i used super-grub to to find elilo.efi etc and it booted up slackware. So booting super-grub2- iso might fix your problem. if not it might be a case of using a live OS to mount and re-install grub2. you can't go far wrong with knoppix 8.6 or 8.6.1
also out of interest if you leave out :
grub rescue > insmod normal
and jump to :
grub rescue > insmod linux