In a published environment, you will need to set the constants in a different way. First deployment it would take the default. But changes made to the constant in StudioPro are not reflected in the published version. That way you don't overwrite the different (UAT/PRD) settings by mistake.
For Mendix Cloud, you can look here: https://docs.mendix.com/developerportal/deploy/environments-details/#constants
For on premise it is different. In the attached picture, taken from the documentation, you will see a Constants menu item: https://docs.mendix.com/attachments/developerportal/deploy/on-premises-design/ms-windows/updating-a-mendix-application/1_stop_service.png. There you should be able to set them individually.
Hope this helps
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