The vast majority of hormones that give you your sex drive and make your dick and balls do its thing are produced in the testicles. So to answer your question, a sharp pair of gardening shears and a nice, big, thick piece of leather to bite down on should do the trick. You might also want to keep a lighter on hand to cauterise everything.
The problem is that when I turned 18, I signed an agreement to have my medical knowledge shared with my parents. So if my doctor notices in my next checkup that I am missing testicles, then my parents would find out. While my dad taught me to sexually repress myself, he is still idealistic and thinks that I can meet my future wife in college which I am a freshman in. Therefore both of my parents would not be happy if they learn I castrated myself.
However if I give you a location on google maps in an area of the woods I take walks in, you can dress in some disguise, maybe as a clown like Pennywise, and attack me, doing those things to me. Then you can drive away from the scene, and it will be on the news that a phyco attacked me, and cut off my testes. However since you will be masked and don’t live nearby, you will never be found and caught by the authorities. In return for this, I will do anything to owe you my gratitude. I will delete this comment after you agree to do so that nobody finds out what really happened.