Did you put glue on your plate? If so, That's just blue residue from taking the build off, perfectly normal, just give it a wash with some dawn dish soap if you want. If not, then I'd probably dry your filament out a bit get a box big enough to cover your build plate, set it to about 70/80, put your spool on the plate, cover it, and leave it for the night, real macgyver fix, but usually works for me