Ponyluver, it is good to see you so keen.
Unfortunately collection/on the bit/roundness and whatever else you want to describe it as, is a far more difficult notion to learn and teach to a horse than say something like leg yielding.
I know it is frustrating when you come here looking for a straight answer but everyone else who has responded to you is dead on in saying that this cannot be taught via the Internet.
You really do need an experienced trainer on the ground, to give you real time instruction and tell you when you are starting to fall into the right track. Roundness is an ongoing process which requires that the horse develops sufficient balance and strength to maintain that carriage over a period of time. Collection is another step up from that, and especially in the Dressage sense of the word, takes many years of correct, hard gymnastic training to achieve. It is also constantly developing, there are multiple degrees of collection, some horses may not be physically able to sustain even a basic level of collection, and we have to deal with that.
If you get told to see-saw/sponge or pull on the reins in any way, or told to strap more leather or metal to your pony's head, disregard that advice.
Can you see how this is something to address with a real time trainer?
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