Hello Neil
Premium V3 as well as specific Premium V3 SKUs are available in some Azure regions and availability in additional regions is being added continually. To see if a specific PremiumV3 offering is available in your region, run the following Azure CLI command in the Azure Cloud Shell (substitute P1MV3 with the desired SKU):
Azure CLI
az appservice list-locations --sku
You can update App Service Plan using **az appservice plan update
**CLI command
az appservice plan update --resource-group <resourcegroupname> --name newcliplan --sku P1MV3
https://learn.microsoft.com/en-us/cli/azure/appservice/plan?view=azure-cli-latest#az-appservice-plan-update
https://stackoverflow.com/questions/76652707/what-is-poweshell-script-to-create-app-service-plan-for-p1mv3