NodeMCU wiring for Serial1?
You can do Serial.swap() in setup() to swap Serial away from RX/TX pin. Serial is then on D7 as RX and D8 as TX (and you can wire some serial module there). 

Bridge with jumper wire D4 pin with TX pin. the Serial1 output will go over the USB chip to Serial Monitor and you will see the prints to Serial1. 

This will not disturb the flashing mode, because bootloader will still listen on standard Serial pins.