Hello, I read from SKY130 website that we can use variable W and L poly resistor but in Magic only fixed width resistors are available. Where do I find the variable W and L poly resistor in Magic?

The widths are fixed because those are the only widths for which there are SPICE models. You can draw any width and length of poly you want, but it might not simulate correctly (it might be fine, but the validity of the models is unknown). You can poke @proppy about getting the continuous models into Sky130, since that provides poly resistor models that are supposed to be correct across a continuum of widths and lengths.

yes, please follow the progress on this issue https://github.com/google/skywater-pdk/issues/380