FSX Deployment Type

It is not possible to migrate from a multi-AZ FSx to a single AZ deployment: https://docs.aws.amazon.com/fsx/latest/WindowsGuide/migrate-files-to-fsx-datasync.html (see "Migrating between two Amazon FSx file systems")

What you could do is leverage the bellow blog/solution and customize the Cloudformation template to do the inverse of what it was intended for. You would then be able to fire up the Cloudformation template and the DataSync process from the command line.

https://aws.amazon.com/blogs/modernizing-with-aws/automate-the-upgrade-of-an-amazon-fsx-for-windows-file-server-to-a-multi-az-deployment/