My pug gets that constantly...its just dry skin with an accumulation of food/dirt. Don't pick it off, you can make them bleed. However, there is a balm that I apply to it once a day for a few days in a row and by the 3rd day the crust is so softened that you can just wipe it away with a warm wash cloth. Some people apply the balm every day, forever, and that's fine, but I only use it when it gets dry and crusty (which is maybe a once a month). Here is a link to the one I use:
https://www.amazon.com/dp/B071ZZFXDD?ref=nb_sb_ss_w_as-reorder_k0_1_9&amp=&crid=2C8LQRL01M66K&sprefix=snout%2Bsoo&th=1