A nice feature added to the platform ..
https://docs.microsoft.com/en-us/powerapps/maker/common-data-service/autonumber-fields
Wish they had added in the classic solution explorer as well, having 2 different interfaces only creates chaos, it reminds me of Windows 7 and Windows RT
Well this has long been awaited for. And how many times I had my customer walking up to me and ask – “I have an existing field. Do CRM provide Autonumber feature? Can I convert an existing text field to AutoNumber field?”.
Till this point my answer was Yes but with a suffix“but” in it.
However going forward you can with the new entity designer in power apps.
So you can select Primary Attribute Number field of your entity and covert it to AutoNumber type now.
Below I open the OOB Account Number field and set the Data Type from Text to AutoNumber.
Short and sweet. Isn’t it?
P.S – Only existing text fields could be converted into Auto Number Type. You can off-course create a new Auto Number Type field.
Hope this helps!
Debajit Dutta
(Dynamics MVP)
Nishant Rana's Weblog 
thank you for sharing
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Works in DEV but not in UAT. The solution in UAT still assigns it as Text.
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