how to update existing vm instances 'availability_zone' field in nova database 'instances' table

Hi, How to update existing vm instances 'availability_zone' field in nova database 'instances' table? It turns out there are many VMs with default 'nova' availability zone, while the hypervisors are with another different target aggregate/availability zone name, thus live migration for these VMs are failing. The strange thing is that the 'OS-EXT-AZ:availability_zone' output from 'openstack server show VM_NAME' is showing these VMs are already with the target availibity_zone name. No idea why we have this inconsistency. Would it be ok to just update database table entry directly to set 'availility_zone' to different value for these VMs? Or there might be better alternatives I am not aware of? Thanks, Hai