Disbudding paste is designed specifically for removing buds that haven't been burned before (and works best that way). However, they most likely need to be done NOW--particularly if they are bucklings. With disbudding paste, as soon as you can feel the horn buds under the skin (feels like a little bump), but before they erupt to the surface is the time to do it. Shave the top of the head for best results and so you don't accidentally smear the paste anywhere it doesn't belong. If you have banamine, give them some about half an hour beforehand. Put a towel on the floor and lay the kid down on its belly and then straddle it and pin its head down so it can't wiggle. Pin it down between your knees just like when using a hot iron.
Wear disposable gloves that fit snugly (loose ones make it easier to make a mistake). Have your disbudding paste, a bucket of clean water and a washcloth, a bottle of white vinegar, paper towels, extra disposable gloves, wooden popsicle sticks, duct tape torn off in strips as wide as your kid's head (2-3), and a sock with the end cut off. Put the sock over the kid's head and pull it back until the top of the head is exposed but the ears are pinned back against the neck. You can pull it back a little more and tape it in place if it doesn't seem snug enough. I've even skipped the sock and just used duct tape.
Once everything is prepared I smear on the paste with a wooden popsicle stick or with a gloved fingertip IF I have snug gloves. I have more control with my fingertip and can do it faster, which is helpful because usually the kid starts struggling after about 30 seconds. If I can complete both sides before then, I'm good. You want dabs of paste about the diameter of a quarter on each bud. Grab one of your pieces of duct tape (I stick mine to the edge of the stanchion) and place it over the horn buds to keep the paste from smearing. Have more than one piece of tape prepared in case you make a mistake. By now your kid will mostly likely be struggling and yelling. If any paste got where it didn't belong, wipe it off with the wet washcloth.
Now you just have to wait those 20-30 agonizing minutes while the paste does its job. Do not let the kid down to be with its mother or friends. It will try to scratch the tape off and it might succeed. I just hold my babies through the experience. Their body temperature will rise and they may start panting for a short while, but then it gets better and most of them quiet down. When the time is up, pin the kid back down between your knees on the towel and put on a fresh pair of gloves. Remove the duct tape and wipe the kid's head with the wet washcloth. Next soak a paper towel in vinegar and wash the kid's head again until all the paste and residue is gone. Vinegar neutralizes the paste so if there is any lingering down in the fur it won't continue to burn.
It's a lot more time consuming than using an iron so not as humane, but sometimes it's necessary if you don't have an iron or aren't sure how to use one. I think the paste is more user-friendly and doesn't take practice to get it right like the iron does. Definitely use banamine if you have it.