How to get the speed graph? Thanks

I am using Trails on the iPhone for speed recording as a reference. I see the speed graph on the app page is very clear and beautiful. May I ask how to output the speed data to my laptop or somewhere? I output the track by exporting a .gpx file. Then I convert this .gpx file to .csv file, but found that the speed information is lost. I will be very grateful if you can help me! Thank you!