Hi
@Chick_Jimin I'm sorry that your cockerel is not well.
Where are you located in the world?
There are several respiratory diseases that chickens can have. Some are bacterial while others are viral.
Sometimes antibiotics may be needed to treat
symptoms, but if you don't have access, then using natural/herbal remedies would be worth a try for sure.
Unfortunately, I am not well versed on using herbs/plants to treat illness, so hopefully you can find helpful information in the following links.
@Hen Pen Jem may also be able to share some of her great knowledge.
https://www.communitychickens.com/3-chicken-ailments-zw02001ztil/
https://www.fresheggsdaily.blog/2013/04/natural-remedies-for-respiratory-issues.html
Do look inside your cockerel's beak to see if there's mucous or lesions that may indicate something like Canker. Tell us a bit more about his symptoms - is he also having watery/bubbly eyes, facial swelling, wheezing, coughing. Is he able to eat/drink?
Any other symptoms you can tell us about along with any photos you wish to share would be appreciated.