How to repair /boot on LUKS encrypted harddrive?

I have a laptop with Xubuntu installed.

At install I chose the full disk encryption option.

But yesterday i accidentally dd-ed a DSL image to sda1 (/boot partition) instead to sdb1 (pendrive).

How can i repair my /boot ?

Hello I tested the following commands in my laptop - yeah I deleted everything in /dev/sda1 and I got it working again - so here it is:

• Get a live-image and boot from it.

- First lets get a clean /dev/sda1 - open GParted; reformat /dev/sda1 with ext2 and don't forget to confirm the changes and then set the "boot" flag (right click on the partition --> select "Manage Flags" --> check the box next to "boot" [this automatically causes the "esp" flag to be set to] --> click the "Close" button). (this was due to "dd-ed a DSL image to sda1" in OP post)

• Now we will prepare everything to chroot into the installed system and then we will switch into it (via chroot):

   sudo cryptsetup luksOpen /dev/sda5 sda5_crypt
   sudo vgscan --mknodes
   sudo vgchange -ay
   sudo mount /dev/mapper/ubuntu--vg-root /mnt
   sudo mount /dev/sda1 /mnt/boot
   for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
   sudo chroot /mnt
  

• Okay let's delete and reinstall GRUB: grub-install /dev/sda apt purge grub-common (have your terminal in fullscreen-mode due to ncurses), this might ask you if it shall delete everything - select yes; now lets reinstall it with apt install grub-pc here select /dev/sda when asked.

• Lastly we need to reinstall a kernel to get the needed initrd.img-* and vmlinuz-* images into "/boot/". We get currently-installed kernels with apt list --installed linux-image-* and now we reinstall this kernel with apt install linux-image-[version-numbers]-generic --reinstall - don't forget to exchange the brackets with an actual version number.

• Almost done; exit chroot with Ctrl + d, or just type exit, and then reboot (via GUI menus or with sudo reboot)!

Used resources:

• https://ubuntuforums.org/archive/index.php/t-1432656.html
• https://help.ubuntu.com/community/Grub2/Installing