I don't know what "restrict settings" means precisely.
In android app settings are accessed from inside the app itself, rather than from inside the system settings app as on iOS (from my limited experience of iOS - apologies for any errors here!). I don't know this phone's message app, but I'd poke around in its settings to see if there is something in there.
If not, there are alternative SMS apps in the play store which do let you control what shows in the pop-up (or even whether there is one). So if the built in one doesn't do what you want, turn it's notifications/popup off (to avoid duplication) and try a different one.