re-establishing HA config

We migrated to a new datacenter. During the Migration we separated our Act/passive HA setup. New DC FGT unit has a different config now and old DC shutdown. What is best way to introduce HA again and make sure the current FGT stays primary and the other FGT doesn't become primary and overwrite the config?

Looks like they just split as both still have HA configured. Should the HA config be set to standalone and recreated, or could I just set the Priority to 200 on device I want to stay primary and 100 on secondary?

What is best approach?