Unfortunately it's not a valid option in az webapp update.
You can use IaC (Bicep/ARM) to do this though, which would typically be my preference.
https://learn.microsoft.com/en-us/azure/app-service/provision-resource-bicep
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Back in 2018 it was asked if there was an AZ CLI command equivalent to the portal function "Change App Service Plan". The answer then was "no".
Has that answer changed in 5 years time?
Thanks
Unfortunately it's not a valid option in az webapp update.
You can use IaC (Bicep/ARM) to do this though, which would typically be my preference.
https://learn.microsoft.com/en-us/azure/app-service/provision-resource-bicep