It is very straight forward. You can see my entire sketch here that uses Serial1 on a Mega here:
The key points: Declare a global variable for MOVI:
MOVI movi(false, &Serial1);
In your setup() routine, start Serial1 with the baud rate you desire. If you do not wish to change your MOVI’s baud rate on the SDCard as detailed in the manual, you can use 9600 which is the default (meant for Software serial. I highly recommend changing it as I have below to 115200 if you are going to use HardwareSerial. MOVI will be snappier that way.)
Good luck with it.