Two potentiometers to control the range limits of a voltage source
simulate this circuit &ndash; Schematic created using CircuitLab

I'm going to make some assumptions.
Input, output, p1, and p2 can all range from 0 - 1.

Seems to match point slope form of a line.

Output = p1 + input * (p2 - p1)

Output = p1 + input * p2 - input * p1

Output = p1 * (1 - input) + p2 * input

I believe this circuit will accomplish this