Creating my own ASIN in another EU marketplace

Asking for help about listing my product of my own brand, in Germany. Product is FBA in the UK. I am trying to create the German listing in DE. I will send separate inventory to the German warehouses, but I need to keep the ASIN the same so the reviews are transferred between the marketplaces.

The automatic listing creation is greyed out. The build international listing does not work, it says I have to create the ASIN first in the other marketplace. It gives me an excel file to download which I have to fill out with the German translations (I do have the translations already) and then upload the file to the DE catalogue, I can’t figure out how to handle the file, what to change on it, where the photos will come from, etc. If simpler, I would rather manually create the listing in DE, however, I am not sure whether the system will give this new listing the same ASIN in DE as in the UK. (The EAN number is of course the same and I would use it to create the listing in DE.)

Is there any advice you could give me on how to go about this? Many thanks, be safe, and I wish everyone great sales.