Changing domains over a VPN session

Our company has 2 separate networks in different cities. We are shutting down Domain B. Domain B will no longer exist, however any user on Domain B cannot change
domain B To Domain A. We get an error
domain doesn’t exist or can’t see it.
Users use a VPN to connect to Domain A
,they connect successfully and they can
ping by computer name and ip address but
cannot change domain names. What are my options besides shipping their pcs here.
I know once I have their pcs on site ,I won’t have any issues changing domain names.
The pcs are in a different country so shipping them here would leave users without laptops for a long period of time.