Below is how you can easily set the blob tier with a powershell script in Azure.

#Initialize the following with your resource group, storage account, container, and blob names
$rgName = "my-rg"
$accountName = "mystorageaccountname"
$containerName = "mycontainer"
$blobName = "myblob.txt"

#Select the storage account and get the context
$storageAccount = Get-AzStorageAccount -ResourceGroupName $rgName -Name $accountName
$ctx = $storageAccount.Context

#Select the blob from a container
$blob = Get-AzStorageBlob -Container $containerName -Blob $blobName -Context $ctx

#Change the blob’s access tier - Uncomment the line you want to use
#Hot
#$blob.ICloudBlob.SetStandardBlobTier("Hot")
#Cold
$blob.ICloudBlob.SetStandardBlobTier("Cool")
#Archive
#$blob.ICloudBlob.SetStandardBlobTier("Archive")