Assalamualaikum
From the replies of the other members, I am confused about what you are really asking as some have suggested to fast. I understood that you have no appetite and want to change in the sense that you want to start eating.
From my experience, as I don't have a very big appetite either, if you dont eat, you will never have an appetite. The less you eat, the less appetite you will have. Simple as that. Eat so that your appetite becomes bigger. Health is a human's most valuable asset, and if you lose that, you can't achieve much in life.
I had a teacher in school, a very good Muslim man. He was very sick, as sick as you can imagine. He used to have very frequent operations and frequent hospital visits. He was my Economics teacher. And he always used to say, you give me your health, I will give you my knowledge, we will do a swap. I used to feel so sorry for him. May Allah (SWT) give him health. Aameen.
We must always remember that our body is an Amanah from Allah (SWT) and we will be questioned for it, so keep it well.
It is all in our hands.
Assalamualaikum