I assume you want to reset a new password of the existing Facebook account.
1. Navigate to www.facebook.com and in the upper right corner of your screen, locate the downward-facing arrow, and click to open a drop-down menu.
2. At the bottom of the menu, click on "Settings" .
3. Find the "Login" section and "Change password" option. Click and create a strong password.
4. Confirm your current password.
5. Click to save your new password.
Except for resetting the password, you should also check out these tips to help you to secure your Facebook account.