Here’s my previous answer to the same question. Another reminder that taking on this work will void your warranty.
In addition to populating J2, you need to move jumpers R34, R36, R38, and R40 to R33, R35, R37, and R39. Those 0Ω resistors route the Ethernet signals to either the pins on the RCM67xx edge connector, or to the RJ45 jack. I’d also check to make sure C8, C13, R11 and R14 are populated.
Digi has used the following connectors for that product:
Yuan Dean: 13F-61JGYDPH2NL
Elec & Elltek Ltd: MJFR0799