Need to update WiFi credentials

I changed my wifi router , So now My Blynk device is showing offline,
I want to know that how I can add or change the wifi " SSID and Password ’

If these credentials were hard-coded I to the sketch when you uploaded it to your device then you’ll need to update your sketch with the new credentials and re-upload it to your device.

If you used a provisioning service like Blynk.inject, WiFi Manager or something similar then the details of how you input the new credentials will depend on which provisioning service you used.

Of course, the other option is to add a guest network to your router (assuming that it supports this functionality) and create a new network with the old credentials.