It’s not that simple. But you can repair things on your RPi if you have (or can make) a second bootable SDCard.

Get your second SDCard with Debian and boot your RPi from that. Get your „broken“ SDCard in a USB reader, insert that in your RPi.

With chroot:

for i in /dev/sda*;do sudo umount $i; done
sudo mount /dev/sda2 /mnt
sudo mount /dev/sda1 /mnt/boot
sudo mount -o bind /dev /mnt/dev
sudo mount -o bind /sys /mnt/sys
sudo mount -t proc proc /mnt/proc
sudo mount -o bind /dev/pts /mnt/dev/pts

cd /mnt
sudo chroot .
sudo rpi-update
exit
cd /
for i in t/boot t/dev/pts t/dev t/sys t/proc t; do umount /mn$i; done
poweroff

With rpi-update only, when chroot does not work:

To check which device is used for the SD card that needs to be rescued: fdisk -l
In my case: /dev/sda

sudo mkdir -p /mnt/rescue/{boot,root}
sudo mount /dev/sda1 /mnt/rescue/boot
sudo mount /dev/sda2 /mnt/rescue/root
sudo ROOT_PATH=/mnt/rescue/root BOOT_PATH=/mnt/rescue/boot SKIP_BACKUP=1 rpi-update
umount /mnt/rescue/{boot,root}