Install the 4700 Ohm resistors on the top side of the PCB, next to the Pro Micro. These pads are marked R1 and R2. You’ll need to install these on both PCBs. The orientation of the resistors does not matter, though it looks nice to orient all of them the same way.
The only reason to install the resistors on the top side is because they're exposed, and will look nicer with the joints on the bottom. After you've finished soldering the diodes, remember to flip the PCB around to install the other components - only the diodes and the RGB LEDs are to be soldered on the bottom.
The resistors are used for I2C communication only, which is used by the OLED display. Some displays already include these so-called pull-up resistors. If you've bought your kit from Littlekeyboards, you must skip this step. If you've bought your own OLED display and do not know whether it includes the resistors already, feel free to wait with this step until after testing your keyboard. If the displays don't work during the test, you can still install the resistors afterwards.
If you’re not using the OLED displays and if you’re not planning on using I2C, you may skip this step.