Hi @yoshihirok ,
Once the Environment is created, the region can't be edited any more.
If you want to build the flow with a new region, you need create a new Environment with the region you want.
If you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
https://powerusers.microsoft.com/t5/Flow-Ideas/idb-p/FlowIdeas
Best Regards,
Community Support Team _ Zhongys
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.