Blynk legacy can't to use

How to active blynk legacy, because my blynk legacy can not to use again

To use Blynk Legacy you wouldn need to set-up your own local legacy server, and find a way to install the legacy app on your device.

Even if you do that, you still have issues with account creation (because the later legacy apps had this feature disabled and email (because Gmail have tightened security and its now much more difficult to use Gmail with local server).
In addition, the local server code is not being updated, so vulnerability flaws are not being fixed, and its not being updated to run on the latest versions of Java.