My method uses Node-Red as the main controller, which runs on a Raspberry Pi and integrates both Blynk and Alexa.
The devices being controlled by Blynk/Alexa are controlled by sending them MQTT messages.
Our problem is that you haven’t shared any information about the Blynk/Alexa integration you’re using. There are many different ways of achieving Alexa control, and therefore many different possible solutions to your issue.