Make u-boot image

Hi, first time post here.

I’ve used my BananaPi with Debian for years now with much effort in configuration. Now, my SD Card is broken and with that my bootloader too.

I was able to rebuild a temporary bootloader by installing a fresh system to an other HDD, but every restart I am forced to enter the bootarg root=… for finding the correct Harddrive.

Guess I’m right that there is no regular bootloader installed, but the Banana has an bootloader fix installed on nand, correct? Therefore I’ve tried to edit the enviorement settings, but it seems like this is saved in some file I cant find (initrd image ?)

For makeing a new image I only found some outdated tutorials. So, how do I make a new image which I can flash on sd card?