Have you tried liver before? You have to be careful about using too much of it, but if that is a high value treat that a lot of dogs go nuts over. There are a few good brands of freeze dried liver, but have also known people who buy raw liver and cook it themselves to make their own training treats. Personally I use PureBites freeze dried chicken because it only has one ingredient (chicken) and can break the pieces into small nibs.
I got a big training pack from Pupford. The salmon and chicken are my pup's favorite, and I love how not dense the salmon ones are--super quick for her to eat. They're also pretty small and low-calorie.
I did try a pack of freeze-dried chicken from the pet store (like these: https://www.amazon.com/Purebites-Chicken-Breast-Dogs-11-6Oz/dp/B000Z3MBRM#:~:text=PureBites%20are%20made%20with%20only,texture%20and%20freshness%20they%20crave.) but they were super big, and made a huge mess disintegrating when I tried to tear them into smaller pieces.
Little pricey but my poodle mix loves these it's 100% freeze dried chicken with no additives. They're his second favorites. He hates the majority of treats especially biscuits and surprisingly a lot of human food except cooked meat and cheese. Another alternative from the same maker of these treats is the freeze dried lamb. He loves those as much as the chicken.
His absolute favorites are these but you definitely have to supervise every time you give a dog a chew like this. Some people aren't fans of rawhides though because it can cause a tummy blockage but in my experience, as long as you don't over-do it giving them too many and supervise that they're actually chewing it down and not swallowing a rawhide whole, it's been fine.
As far as training, there's plenty of youtube videos that can assist you. I'm always a fan of positive reinforcement with clicker training, praise and treat based, gotta find the right treat though. I use small bits of mozzarella cheese because that's the only thing that gets him to pay attention to me outside with many distractions. Really just have to find the right motivation that works for him through trial and error.
I'm not a pet trainer but I've hired one before but he's based up in The Bronx and while it was great to get personalized individual attention, and I'm grateful for that trainer working with me especially with my dog's food aggression, I feel that many of his tips you could research yourself and see what works and doesn't work for you and the dog if you have the time to put into it.
Freeze-dried chicken and Plato Small Bites are my go-to shelf-stable treats.
Not the healthiest thing, but for occasional high-value treats little bits of bread are Badger's favorite.