If you want to uninstall FixMKVGaps , proceed in two steps:
1) First restart the application, type F10 to go to the settings page, then click the Preferences tab. Click Do not save when quitting.Then you exit the application (answer None if you are asked if you want to save your preferences). In this way, you will completely erase any data that the application has written to your system, either in the Windows registry or in an ini file.
2) Then you have to delete the executable file like fixmkvgaps_xxfr.exe that you copied to a folder during the installation. Normally you send it to the trash.
If you follow these two steps, you are sure that no trace of the presence of FixMKVGaps will remain on your system, except of course any _fixed.mkv files you have produced, or sometimes some temporary files of timecodes of the form xxx_trackn.txt that will have been created in the temporary folder of Windows and that you can delete manually.