Yesterday I did my first 200K of the season. Due to operator error I ended up with two files, one for 110 miles, and one for 20 miles. Is there an easy way to merge them into one? I searched the Google machine but couldn’t find a working solution.
I recorded both rides on a Garmin 1030 Plus. Both are available in Garmin Connect and synced to TR and intervals.icu
Try File Combiner
The above is the easiest file combiner especially with .fit files (the default for most garmins and probably other gps units too) to Strava/TR. I havent had success with it to GC for that I use Combine FIT, GPX, CSV or TCX files for Garmin or Strava. Merge Heart Rate Power and GPS (gotoes.org)
Most times I don’t bother about combining in GC (Just Strava) and use fitfiles 
I used Goties recently to merge data from dual recordings.