Transfer licenses into another Craft ID account I could only transfer licenses that were not yet assigned to any other Craft ID account. But how can I transfer the licenses, which are assigned with my other Craft ID account?
You will have to release the license in your Craft ID account:
https://id.craftcms.com/account/licenses/cms

After that you will be able to claim the license in your other Craft ID account:
https://id.craftcms.com/account/licenses/claim