Selecting potentiometer for adjusting Vo in DC-DC step down
The values for individual trim up/down resistors assume a known resistive loading at trim input pin. They shift the voltage divider ratio that is present between the sense and trim pins.

The fact that no value is given on p33 of that data sheet for the potentiometer method implies that the value of the pot is not critical. This pot will adjust the voltage divider ratio.

It should be possible to compute what the reference voltage is, and the resistor ratio behind the trim pin, from the two calculations. However, that's not necessary.

I would use a 10k pot, as the value is much less the existing behind the trim terminal appear to be, given the values calculated. A 2Mohm pot would also work, but I suspect you would find it did little in the mid range, then got a bit vicious towards either end.