If you are able to get your hands on a OBD2 code reader/scan tool or Forscan, a DTC would be most helpful.
Otherwise, these App notifications tend to be somewhat vague and generics. That's why it says "for vehicles with capless fuel system) vs giving you a targeted diagnostic. Certainly feel free to try to insert the funnel and see if it helps.
However, just an FYI the actual reason may be completely unrelated. Ford just throws something like this out there because it's simple and the owner can try it themselves. It may not be the correct action to take however. I believe the EVAP purge code will pull up a similar "recommendation" that will do nothing to fix the problem.
Long story short, you really need to get the DTC number as the first point of troubleshooting this.