Try a different video hosting site to see if you've got the sound there. (This DailyMotion link is as good as any: https://tinyurl.com/yccm2c8v )
If you get sound there we'll know that the problem is specific to Youtube on your iPad. If you don't get sound there we'll know that it's a problem with your iPad itself.
If the Ipad is anything like my computer. When youtube - there is a speaker volume thing/button on the actual screen, but i do have another option at the bottom of my computer where there is a little symbol of loudspeaker. When I click on to that - there are little equalisers that come up that allow me to volumise more and unmute from there as well. Hope that makes sense
I've got it back, after numerous attempts the unmetered button worked, but only for each video. So I have to unmetered each time I want to watch one.
Thank you all for your help and suggestions.