Minimal BASH like editing is supported

[ObscurityPrince]

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[ubfan1]

From the live CD, take a look at the EFI partition and the file /EFI/ubuntu/grub.cfg. It probably uses a UUID for your (old) Ubuntu root, which changed when you resized. Use blkid command in a terminal to get all the UUIDs, locate the one for your Ubuntu root, and edit that one into the /EFI/ubuntu/grub.cfg . Or maybe all it takes is to reinstall grub.

[ObscurityPrince]

Thanks ubfan1 for the reply. How though do I access the file /EFI/ubuntu/grub.cfg from the live CD?

[ubfan1]

Mount the EFI partition (Use /mnt as a mount point unless it's not empty, otherwise, just make a directory under /mnt and mount there). Assuming your EFI is on sda1 below.
sudo mount -tvfat /dev/sda1 /mnt
Then you should see the EFI directory under /mnt,:
ls /mnt
EFI
So change default directory to
cd /mnt/EFI/ubuntu
and edit the grub.cfg file.

[ObscurityPrince]

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