According to this list on Wikipedia the only launches to a Heliocentric orbit were DSCOVR, TESS and Elon Musk's Tesla Roadster. No other SpaceX rocket went beyond a geostationary transfer orbit (GTO). In launches to GTO the second stage is typically left in a decaying elliptical low-Earth orbit, until it re-enters the atmosphere. (see e.g. here, here or here)
DSCOVR was sent to the Sun-Earth Lagrange point L1. Without station keeping this Falcon 9 second stage will have left this point and is now in a heliocentric orbit.
TESS was launched onto a lunar flyby trajectory, after which the Falcon 9 second stages was placed in a heliocentric orbit.
For the Falcon 9 second stage, the day was not done at TESS separation as SpaceX planned to dispose the upper stage into a heliocentric orbit by firing its engine a third time to escape Earth’s gravitational influence.
And of course Elon Musk's Tesla Roadster is on an elliptical heliocentric orbit that crosses Mars' orbit.
Planned SpaceX missions to heliocentric orbit are DART and Psyche (with possibly Janus as secondary payload).