Reinstall Whatsapp without restoring the group contact

Hi,

Open the group chat and tap the group subject, then you can remove the contacts from the group. Alternatively, delete that group and recreate a new one.

If I understand, you're trying to leave a group without notifying the admin? If so, I'm afraid it's not possible... Apparently, even if you delete your WhatsApp account without leaving the group, the admins will still be notified that you're no longer part of the group. The other members will never be notified when you leave a group however.