Swapping out a PCB is a simple process but should be done carefully to not damage other components in your TRMNL.
First turn off the device. Then open it up (video guide), laying it flat like this:
Next, use a small Phillips screwdriver to remove the 3x screws on your PCB. A flat-head also works but you'll need to be careful to avoid stripping.
After removing all 3 screws, slowly lift the board and detach the battery by pulling straight outward on both wires (red/black).
We're almost done. Use a finger nail or screwdriver to "open" the black gate, located along the back edge of where the ribbon cable attaches to your board.
This will allow the ribbon to slide out of the board. Here's another angle.
You may now replace the board. When inserting the ribbon cable to your new PCB, be sure not to insert it diagonally.
Here's another example, with the board inserted at a diagonal angle. This will not function.
So insert the ribbon cable straight, but note that the gold section of the ribbon cable will not be completely covered by the white/black connector.
Seeing a narrow, even width section of exposed gold pins is the expected installation.
Now you can lower the board back into place, re-attaching the battery. The red wire should be on the side of the USB-C cable.
Finally, add back the 3x screws. We recommend starting with this one first, as it will help "seat" the PCB into the tight tolerances of the enclosure.
Close your case (video guide) to complete this procedure. Turn the device back on, then re-pair WiFi and add the device to your account as if it were brand new.