Hi! Welcome to YT!
I've never seen a yorkie/lhasa apso mix before. I bet your pup is very cute. You should share pictures sometime!
How I taught both of my dogs to walk on a leash is by first, buying a harness. Harnesses work great for little dogs. Your puppy is a mix and I'm not sure if Lhasa Apsos are prone to tracheal damage, but just to be on the safe side I would switch to a harness
Collars are known to be damaging to the trachea of small dogs.
But I would attach the harness and leash and I would first let my pups walk around the house on their own with the leash attached. I would throw balls and play games and just get them used to the leash being there and the feeling of the harness on. I would also give lots of treats
. I would do that a couple of times just to get my pups used to the harness and leash. After that I would then take them outside, holding their leash, and start walking around. If they wouldn't budge I would set the leash down and walk off. If they started to follow me I would then pick up the leash and keep walking. If they would keep walking with me I would reward with praise and treats. If they wouldn't keep walking with me I would set there leash down and start walking away from them again. I kept repeating this process until they would start walking with me.
At first, your main challenge will be just getting your puppy to walk while on a leash. Once your puppy has accomplished this than you can move on to leash training (not tugging and pulling).
Good luck!! I had luck with training both of my dogs with this process, but it might not work for every dog. I know there are plenty of other members here on YT that will have great advice for you!