Welcome.
You didn’t mention what methods you have tried so far to do such “blinking” of a GPIO, but it is fairly easy to do with a nested timer and adjusting the timed ON, OFF durations as required.
Put this BlynkTimer code into a BLYNK_WRITE(vPIN) Function, controlled by a button using a virtual pin , and you should have what you want… just change (or add to) the Blynk.virtualWrite() commands for digitalWrite() of GPIO pin. The OFF condition of the button will need to run two commands that disable the timers.
Otherwise… A lot of reading and testing out of the various examples will be a recommended start.