We have requirement to change email address, so we have modified change email screen-set based on our requirement where we have added new email, confirm email and password. I have attached a screen for your reference.
So our query is that can we validate a password which user entered from a screen with the existing password of registered user, can we validate a current password?
It looks like you want to validate password before a user updates their email address.
You can achieve this by using a Re-Authentication flow:
Basically you prompt the user with a login screen (they can use password but also any other supported authentication method) and once they successfully reAuthenticated you can direct them to a profile update screen where they update their email.
Hope this help,