I know nothing about these matrix boards, but presumably there is some sort of library available which allows you to send them text from your device (let’s say that’s a NodeMCU for now).
The library will have example sketches, maybe including one that scrolls some hard-coded text, runs through some different scrolling examples, changes colours, speeds, font sizes etc etc.
This type of thing is fairly typical for libraries for various LCD, TFT and OLED display libraries for devices.
Your task will be to modify these example sketches so that instead of the text, colours, scrolling speed, scrolling direction, font size etc being hard-coded in your sketch, the values that are used will be inputted via the Blynk app.
Your NodeMCU will be connected to the Blynk server as well as controlling the display, and you will use virtual datastreams and the appropriate widgets attached to these in the app. When you update a widget in the app it will trigger the BLYNK_WRITE(vPin) function for that datastream, and you’ll retrieve the value that was inputted via the app and use it to change the corresponding parameter in the code that controls the display panel.
Your first task is to find a C++ library for these display panels, and run the example sketches to ensure that it works as expected,
Then you need to work-out how the various parameters that you wnat to control are changed within these examples so that you can display your own hard-coded text etc.
When you have this working and you understand how the library works the you can look at adding Blynk into the equation, so that instead of these parameters being hard-coded into the sketch they come from the Blynk app.