Select the region(s) you want to use and disable the use of other regions in multiple accounts using AWS Organizations through Service Control Policies or if you have deployed AWS Control Tower select the regions to use and block the rest in the Landing Zone configuration.
Documentation site with policy examples
AWS Global Infrastructure Regions
More Information about Service Control Policies is available in a related recommendation here
AWS Organizations service as well as Service Control Policies are free.
AWS Control Tower has no additional fee, however, you pay for the costs of the services that AWS Control Tower enables such as AWS Config and AWS Service Catalog.
More details here: https://aws.amazon.com/controltower/pricing