Okay, so you more than likely have a three-wire running up to the fan. It’s entirely possible the second switch was wired for the light but just not wired on the fan side.
Test to determine which of the two conductors of the three-wire powers the fan. That conductor goes to the load terminal on the switch. Remove the conductor from the traveler terminal. Cap off the unused wire in the switch box.
Make sure the switch is sent to the on/off mode.