I guess the OP wants an instant removal of the queued recruits thereby recovering all the associated food.
Well It seems the only way to do that is to step wise press on the minus button, just the reverse of the queuing up process, not sure there is other method.
I think TC11 is the cheapest TC food-wise. Dumping them into another TC will end up costing you food. If you have a surplus in TC20 you can pull them and dump into TC11, then you get a net gain in food.
I am not aware of any way other than TC’s to dump recruits.
This game is not made to do anything very fast. I recommend eventually stocking a TC 20 so when you need food it will be stock piled there. It’s 100 recruits and 297k food. It definitely comes in handy when you need it. Setting up training camps can be crucial to they way you play the game.
I use the system of 3 TC11’s and just let them run. I don’t feed out of them for days while I stock my one TC 20. Once I have a couple hundred ready in each of my 11 camps I also have the food stocked to level a hero quickly. Harder to explain than to do🤪
As @Rigs clearly pointed out, minus button is the only way to remove recruits. However, the problem lies if you have a huge number of unused recruits and you are planning to remove some of the queuing trainees to enable you to use the food, specially from TC20 functions. If you force to do so, you will just waste the food and some recruits. This only needs some TC management. The most common strategy is at least one of the four training camps is used for TC20 function, while the rest are for TC11 function. TC20 will serve as your piggy bank for recruits and food. TC11 not only provides constant production of feeder heroes, it also allows you to use it as dumping ground of the cheapest recruit with minimal cost to food and recruit. And if you have decent enough number of swords, backpacks or rugged clothes, you can convert two TC11 to work on any of the TC1 (swords), TC2 (backpacks), TC3 (swords) or TC19 (rugged clothes) functions, depending on the availability of swords. I usually get my two TCs working on TC1, TC2, TC3 and TC19 functions whenever I have several hundreds or thousands of the needed materials and that my TC20 is queued for more than 300 days where food and recruits are stored aplenty. My other camp working on TC11 function may be used to pull out some recruits. This is how I manage food and recruits. You can definitely do your own thing with just a little planning.
Even I as f2p am reaching a point where recruits are getting surplus. I have a TC20 and a TC11 at over 200 days (which I realize is nothing compared to others) but that has doubled for me in just a few months and with the shortage of 4* AM will likely only continue to go up.
As has been noted above, you use the TC20 to bank food and the TC11 to bank recruits. If you need a bunch of food for an expensive ascension, upgrade, or just to craft battle items, you move the recruits out of TC20 and add them to the TC11 and then spend the surplus food on whatever you need.
After using about 20 WE flasks on the last AR, I currently have a 60-day supply for my TC20 and 408 days on my TC11. I have a bunch of 4 and 5*s to level up from my last 10x event summons and Atlantis summons, so I’m running my other two camps at TC2 until I run out of backpacks (currently a 6-day supply each with 500 backpacks remaining) and putting all my new recruits there.
Even with a good strategy to use the TCs, you’ll have some ridiculous long queues of trainings with no chance of ever finishing one of those. It’ll take hours and hours just to move all trainings from one to another. It’s annoying and should be advanced with some cute automation.