your remote access vpn into the office needs to also connect whatever subnets you are using the the GCP vpn so that the remote workstation has a route to the resources.
you will then also need to nat your remote vpn pool to the local office subnet for traffic that goes from the pool to the GCP subnet. This will allow the traffic to pass the GCP vpn.
you also need secuirty policies that permit this communitcations.