Currently, this can only be done manually in the iOS source code before publishing your app.
If we are publishing for you, please simply request this change as part of your publishing instructions.
You must change one file in the source code, to change the viewport from user-scalable=no -> user-scalable=yes.
After opening the source code in Xcode, please edit LEANUtilities.m file. You can search for "user-scalable=no" and modify it to "user-scalable=yes".