OK, I think I have it figured out. The middle pot does nothing but set the point (based on current) when the 'charge' LED turns off and lights the 'OK' LED. The board does not shut off when finished, but when the cell voltage is equal to the regulator output voltage, no current will flow.
Set the open circuit voltage to 4.20v, 4.30v, 4.35v, whatever.
Short the outputs with an ammeter, adjust the current pot to the desired 'end current', or the amperage where you want the LEDs to indicate charge complete - say .1A. Then adjust the middle pot until the middle 'CH' LED just turns off. During the charge when current to the cell falls below that point the LEDs will change.
Short outputs again with the ammeter, set the max charge current, say 1A.
At the start of a charge cycle with a flat cell, current will be limited to 1A (the cell would take more than that, if it weren't limited). The far right LED (marked 'CC/CV') will be on, and the middle 'CH' led will be on. The 'OK' LED will be off. In this pic the 'CC/CV' LED is red and on dimly, the blue 'CH' LED overwhelms the camera:
In the middle part of the charge the current into the cell will fall under the 1A limit, the 'CC/CV' LED will turn off, middle 'CH' LED stays on.
Near the very end both 'CH' and 'OK' will be lit together:
When the charge current falls below the set point and cell voltage has risen to the voltage set point, the 'CH' LED will turn off, with only the 'OK' LED on:
The cell isn't completely finished at that point, but, since output voltage can never go over your setting, if you set it to the correct voltage it should be ok to let it run like that basically forever, I suppose. For a 4.30v setting if you remove the cell as soon as the 'CH' light turns off, cell's resting voltage will be around 4.26-4.27v. Another 15-20 minutes will bring it up to 4.29-4.30v.