You should be able to plot the ROH using karyoploteR. You can find information on how to use it on the vignette and a tutorial and some more complex examples with step by step instructions at [https://bernatgel.github.io/karyoploter_tutorial/].
It might even automatically read the output from plink with the toGranges function. If it does not work, you can give me a few lines from the file and I can try to guide you.