you should have an electric bridge device to do that (like four probe bridge). here you have two options either by preparing a paste (like IR paste) of known thickness or by thin-film measurement. if you decided to make thin film you have to measure the bare substrate first then your sample (substrate +film) and you have to know exactly the thickness of the film and substrate. These may help you too:

https://onlinelibrary.wiley.com/doi/abs/10.1002/j.1538-7305.1961.tb03245.x

https://www.researchgate.net/post/How_can_I_measure_the_electrical_conductivity_of_thin_film

Hope you find this useful.