I can't find the Video presets folder. I have followed instructions and even exported a video and this is supposed to automatically create it but it's still not there.

Any advice?

Thank you.

You could try creating it yourself, it should be:
C:\Users\<your userfolder>\AppData\Roaming\Adobe\Lightroom\Video Presets

You could try creating it yourself, it should be:
C:\Users\<your userfolder>\AppData\Roaming\Adobe\Lightroom\Video Presets

Sorry, I don't follow. Is that for PC? I'm on a mac.

Can I not simply create a subfolder in the in LR Presets Folder and call it Video Presets?

Yes thats for PC. It should be similar for mac. Find the presets folder (in Lightroom in the options dialog, 2nd tab), and create the folders.