A couple of pointers…
Blynk is predominantly an IoT application… That stands for Internet of Things… emphasis on the word INTERNET 
That said, it is possible to have a Blynk interface running on a Local Server with total internal networking… but for that to work, you need your Local Server to also act as a Wireless AP and you connect your phone to it, not to whatever service you normally use.
This is not beginner level stuff and there is no drop-in code to offer… Like transitioning from walking to driving to flying, you need to start at the ground level and work your way up 
So first…
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Have you been able to control the motor with “normal” Arduino/C++ code? This is a must, as Blynk will not directly control your motor, only pass on commands from the App to whatever motor controlling code/hardware you already have.
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Have you been able to use Blynk, with normal Cloud Server, for anything? - This is a requirement to start learning how Blynk works before trying to merge it with pre-existing code… let alone a fully independent AP/Server.
If you have all that prior experience and code under your belt… then you can search this forum for a topic or topics of setting up something like a RPi Zero W as a full AP/Blynk Server.
We can assist with any Blynk related questions as you learn. Happy Blynking 