@Stephan Mühlstrasser Thank you for reaching out to Microsoft Q&A. I understand that you want to change the tier for all blobs in a container in one operation from the Azure website. This is not possible from the portal at the moment and has to be done one by one.
If you want to do this as a bulk operation, I would suggest that you use a script that can do it for you. Here is a link that has an example for the same- https://xenit.se/blog/2017/12/21/azure-archive-storage-manage-access-tier-blobs-container/
Hope this helps. Please let us know if you have any more questions and we will be glad to assist you further. Thank you!
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