How to adjust the voltage of this SMPS?
Strange. This is a single supply module, yet it has two switchers on board.  

Anyway. Yes, connect a voltage between 3.5V and 28V to the input and measure the output voltage, which you indeed should be able to adjust with the multiturn potmeter. 
Check the switchers' datasheets for the maximum output current. The right IC seems to be an LM25005, that can deliver 2.5A. May be a bit high for the coil though. The left one I can't read.