WooCommerce Checkout page make additional notes required

Hopefully somebody can help, I have been setting up the checkout page for WooCommerce on the customization panel and I would like to make the Additional Notes section mandatory. I would also like to add into the notes box the text "please tell us the model and year of your car"

I have checked the Theme Editor but cannot find anywhere that appears to control the checkout page.

I admit my coding level is low, it may well be I am not looking in the right place.

If this is possible (it has been achievable on other themes I have used) I will very much appreciate some instructions for how to do it.

Many thanks