If on Android you could use this type of app - https://play.google.com/store/apps/details?id=com.lexa.fakegps&hl=en_GB&gl=US

On iOS you could turn off location services to prevent GPS from working rather than spoof, or deny certain apps location permissions which might mean it reverts to other forms of geolocation like IP

There are probably methods to spoof GPS on iOS too but sort of a separate function from a VPN