Can't export extended columns of user through powershell script

Hi,

I have created multiple extended column on user schema in my azure active directory.i want to try to migrate the users from dev environment to test environemnt which is another azure ad.but when i am trying to export users through Get-MsolUser command its returning only selected columns not the extended column when i  specially mention the name of extended column in command like "Get-MsolUser | Select-Object extension_0f454354534534534534eaa2743e65_textid" it return null.in the same way its also not importing value to these extended column giving error that not able to find the column name.So how can we export or import the extended columns from azure ad.

Regards,

Ashok