Guitar string frequencies are 82 Hz, 110 Hz, 147 Hz, 196 Hz, 247 Hz, and 330 Hz. Generate each frequency and twist the knobs until you can no longer hear a beat frequency.
Or buy a tuner.
If the strings are hard to keep in tune you will want to replace them. In that case google "change guitar strings".
Then you search "smoke on the water tab", and you should be good from there.