Do you mean the hygrometer, which is used to check the humidity?
I don't know how to calibrate a thermometer unless you know of a place where you absolutely know what the temp is.
To calibrate a hygrometer you put 1/2 cup of salt mixed with some water so it looks like a slushie in a ziplock bag with the hygrometer for 24 hours and it should read 75%. Don't let the hygrometer touch the salt/water mixture.