Ok I´m done.

Thank you very much for your quick advice.

The documentaion is kind of misleading.
"The /uninstall option may be passed to immediately begin removing Python - no prompt will be displayed."
Because of the last part I thought the /quiet is included and not necessary for the uninstall.
After I found the registry entry from "Python Launcher" I get the uninstall cmd.

Maybe you could still tell me something more about the /passiv?


That is what works for me.

Uninstall Python3.7.3:
PathToPython.exe /uninstall /quiet

Uninstall Pythonlauncher:
MsiExec.exe /X{A28C27E4-A725-482A-9C65-61EDC0E4D583} /qn

ciao