Hi Sremrofsnart,
I’ve sent you a pm but this maybe of some help for anyone else trying something similar, there are 2 tools I use Avidemux and Kdenlive both are free and very good to use but can take a little research to get going.
Avidemux: if you open your file and once it’s loaded to the left you got video and audio settings, there is a ms toggle with up and down arrows on to adjust the audio you can play back in the app to see if it has synced correctly and keep adjusting until satisfied.
If you are happy once you have made the correct adjustment you can press the save icon and viola.

Kdenlive - drag and drop your video and audio source into the project bin and then from the project bin drag the video into your project timeline underneath and then the same with the audio but putting it under the video in your project timeline, now you can slide the audio clip left or right to sync it to the video and playback in the app to make sure you are happy with results before doing any rendering.
Once happy at the very top click on project, scroll down to render and select audio only (save having to render the video which will take longer) once done use a tool called Mkvtoolnix to mux your newly synced audio to the video and 🙌.

Hope this is of some help or to anyone else who is struggling with something similar, there maybe better options out there but those are the ones I know of.