(enable dev settings)
1. Go to "Settings" · 2 Tap "About device" or "About phone" · 3 Tap “Software information” · 4 Tap “Build number” seven times
you'll see a wee toast msg bottom of screen telling you dev settings are now available
Settings > System > Developer Options or Settings
other open source mock location apps are available
https://alternativeto.net/software/fake-gps-location-/