I took the tank to Riga kinda grey/black market for useless parts and weird equipment (unofficial marketplace, created after the soviet union collapsed and somehow still exists). I found a specialist there on gas tank equipment and apparently I had bought a specific tank for refilling sodastream like devices with a different name in Europe.
His solution was to change the valve. But he was concerned that below it there would need to be a special screw like pin (I'm not using the right english terminology here). Anyways it was clear that an adapter like that doesnt exists.
So I emptied the tank manually, using a small screw driven into a large wooden table (outdoors). And then removed the built in valve. Under it is a standard thread. So now I just have to buy the standard valve to replace the one I removed (a few bucks) the regulator (also a few bucks), and the bottle holder. So a pretty cheap solution. Also gotta refill the tank, but there are many services for that available and my quantities are negligible.
Sorry for long post and bad english/wrong terminology. I just wanted to post this so if someone comes across this problem his solution is to simply empty the tank and remove the valve and then change it. The 1l tanks (from sodastram like devices) top valve part is unique and is the problem but the built in hidden part is completely standard. If you know the right place to buy these parts it will cost you nothing, just have to empty manually and then replace the details.