Send corrections to a GPS receiver from RTKData.online. Create an account there to use. AOG setup: username (blank), password (blank), url rtkdata.online, mount (your mountpoint), caster port (your caster port). Edit the code to enter your mount point, caster password and serial port connected to the receiver. Upload the code to a Teensy4.1. Upload the F9P base settings using Ublox U-Center. Edit the F9P settings to enter the fixed location of the base.

A spare autosteer board will work for this.