Everything is a compromise.
First question is how far off are you? If you're a few KB over, then there are likely to be some options, but if your video is 8GB (Facebook's limit is 4BG) then you're going to have to rethink your approach.
In terms of options, let's look at what you can do:
the most obvious one is resolution. Anything above 720P is pointless since FaceBook will rescale the movie to 720P for playback. If you're exporting in 1080P that's a lot of savings (1080P videos are typically 1.5-2x the size of 720P, so that 8GB 1080P movie might drop to 4GB at 720P).
Second option is frame rate - if your presentation doesn't have too many transitions/animations, then you can drop your frame rate. Most presentations are mostly static, with transitions between slides, so dropping to 24fps (or even lower) can help, without affecting the user experience. Not an option if your presentation contains full-motion video, but Il working blind here :)
The Format choice is worth playing with, since different codecs perform better with different content, and I don't know what your presentation looks like. HEVC is a good all-round option, and generally produces smaller files, but H.264 might work better for your content, so it's worth trying.
If none of that works, you may need to look at your slides to work out what can give. Check things like background colors (solid colors will compress better than gradients) and remove any extraneous content, animations/transitions, etc.
If that still doesn't work to get you under FaceBook's 4GB limit then consider a different platform such as YouTube (256GB limit), and just linking your video to your Facebook page rather than uploading directly.
