I don’t know of a solution on iOS. There are a few ‘kiosk’ apps for iOS, but I’m not sure if any of them have the option for remotely changing which dashboard URL is loaded. Perhaps you could ask over in the How to switch from Android/Fire to Apple / iOS / iPad Pro? - #2 by josh thread to see if anyone who uses those apps knows. Or even reach out to the app developers to get their insights.
As a point of reference, the Fully Kiosk and WallPanel apps for Android each have a REST API which can be used in a rule to control which URL is displayed. If any of the iOS kiosk apps offered a REST API, my thought was you could use that to control which dashboard was displayed.