Did you use the Blynk Edgent example, or an example where you hard-code the SSID and password into your sketch?
From your rather disorganised description, I guess it was the Edgent example.
The ‘nuclear’ way to remove stored data, including WiFi credentials, from any ESP device is to re-upload the sketch and in the Tools menu choose Erase Flash : All flash contents.
Edgent is designed to allow the credentials to be cleared by pressing a button for 10 seconds. But, this only worked if you in-commented the appropriate board definition for your board type.
More on that here…
Pete.