Get them working from behind first start with a 20 metre circle and slowly make the circle smaller then leg yield back to 20m circle
dont focus on the head. collection comes from the hind. get a proper working hind and the headset will follow naturally
Peppermint Bit Wipes by Horse Armour are always a nice way to get your horse to look forward to the bit. (they also come in apple its pricier though)
Get them supple and loose and then then work on them going onto the bit, do lots of snaking around, bending etc
The same way you would get a horse that isn't stubborn to be on the bit. Is there anything in particular that your horse is protesting to?
My biggest recommendation is to include a correct rein back in your workout.