Do you know the part of the potentiometer they use for the fine trimmer? There is probably a digital potentiometer you could drive (via SPI typically) via the Arduino.
The link to the bill of materials doesn't actually provide a list of parts...but if you know the part number a digital substitute might be identified.
That one only has 129 steps so if you intend to sweep it in a logarithmic way like the original the steps will be quite course in your "fine" trimmer
It can deal with the power (400mW is rated higher than the 250mW of the manual one). Unlike the manual one the setting is volatile, so it will forget where it last was on power off. There are types that are non-volatile if you prefer, alternatively you'll need to code around its lack of memory by storing something in your Arduino EEPROM for example and putting the potentiometer back to that setting on startup.