Hi,
Diodes like 1N4148 / 1N914 100ma and 1N4001 to 1N4006 1amp, will drop the voltage by about 0.7vdc.
There are other types of diodes that will drop the voltage by just 0.2vdc
You can buy them for a few pence from Maplin stores or any electronics shop.
Being as you are talking about dropping 5v to 3.7 you will need at least two diode in series.
Before connecting both units together you would be wise to test the voltages before and after the diodes to ensure the voltages are ok
However I do not know that equipment, and if the author cannot clearly show what is actually needed I would be dubious about connecting anything like that up, unless you can get some first hand confirmation of what is needed to guarantee it works.