Once at Railroad HQ, speak to Desdemona and agree to her terms.Give the Courser chip to Tinker Tom, who will crack the encryption and provide the code for the chip. Expert help and a lot of resources will be needed to construct it.(One might be able to catch him en route to speed up the permission check; he will be tagged on the Pip-Boy for his entire journey.) The easiest option is to wait/sleep for about 8 hours for him to appear at the settlement or simply build at Boston Airport if using the Brotherhood for help.
Maxson might camp at allied settlements for the night along the way.I have the Courser Chip, but I don't know how to decode it.