Redmi note 10S unlock my phone

All you need to do is to enter you phone number or email address that's linked to your Mi account here to reset the password.

https://account.xiaomi.com/pass/forgetPassword

i forgot my mi account id and password ,i reset my phone and still the device is locked and says the account doesn't exist on the number what can i do now

You can try calling the local Xiaomi helpdesk to seek help.

Or you can bring your phone to the nearest Xiaomi service center with the purchase receipt to ask them to reset everything for you.