Video is much more processing intense than audio, so common for audio to get ahead of video when processed separately (ie video from camera, audio from your mixer).
- Simple solution (which will hinder your flexibility) is to join Audio to Video before reaching OBS Studio. For example, we could plug Audio into our NDI PTZ Cameras
- Audio video sync is a common issue when that follow separate data paths. There are numerous tools to adjust, which for you to use... depends. Personally, I found and like using 
https://streamgeeks.us/fix-audio-sync-issue-in-obs/ to identify the amount of lag. Ideally the log will be consistent. If lag varies, that can be a sign of an under-powered computer for what you've asked it to do.. (fixing could be a simple optimization, settings, adjustment, removal of some unnecessary background processes, or new PC... depends)
Plenty of us running House of Worship systems here who are happy to help