If you are running your app on the Mendix Cloud or SAP Business Technology Platform, you can access these settings in the Developer Portal via Environments > Environment Details > Runtime > Custom Runtime Settings. For more information see:

• the Runtime Tab section of Environment Details for information about the Mendix Cloud
• the Runtime tab section of SAP Business Technology Platform for information about the SAP BTP

When you are running your app locally, you can set these values in a Configuration.

For more information read:
https://docs.mendix.com/refguide/custom-settings/

https://docs.mendix.com/refguide/tricky-custom-runtime-settings/