Please, note that each case might be an individual issue, and these recommendations can be the first step to solve it.
First, please, check if the desync appear in other media players (you can try free VLC Player), and on the preview in the program.
1) If your original video is in sync with audio on the program preview window.
On Windows OS, turn off Intel and/or NVIDIA or Intel hardware accelerations in the Settings of the program (if enabled):
If you have Mac OS, disable the SuperSpeed option in the product menu Settings - Preferences - Acceleration menu.
If the issue persist, try selecting any other output format or change video and audio codecs in selected format settings.
To access format settings, click the cogwheel button.
Select different codecs at Video tab and Audio tab:
Then click OK and convert the original file again, and check video and audio sync in resulting video file.
If de-sync still occurs after changing output format/adjusting program preferences, please, contact us so that we could investigate the issue further.
2) Your original video starts to desync on the preview.
If you are a PC user, updating your drivers might also improve the performance of the application.
If you are a Mac user, please try closing all the unnecessary applications.
If the problem does not reproduce in any other player, we suggest contacting us and describing the problem with as many details as possible.