Hi Kashifameen,
Thank you for using Apple Support Communities. I understand you're having difficulties with changing your information in the Health app. I'd be happy to assist.
I'd recommend you take a look at this article related to modifying your information within the Health app: Use the Health app on your iPhone or iPod touch
Specifically, take a look at this section:
"Set up your Health Profile
Open the Health app and tap the Summary tab.
Tap your profile picture in the upper-right corner.
Tap Health Profile, then tap Edit.
Add your information, like height, weight, and age.
Tap Done.
You can also set up your Medical ID or register to be an organ donor from your profile. "
Thanks and have a great day.