Can't press the lower right corner of the screen

I bought your Prying and Opening Tool Assortment and followed instructions on your site to replace the home button. Thank you for the detailed instructions. Surrounding the home button, my tablet had quite a bit of melting black substances (plastics?). It didn’t look as clean as your image instructions. I didn’t make any attempt to clean it or anything, but just replaced the home button and reassembled it again.

Although I replaced the home button successfully and the tablet functioned normally, but I am wondering if those melting black substances caused me to unable to select anything in the lower right corner of the screen (like Menu, Close All options, etc).

What are those black melting substances and how can I make my lower right corner of the screen function normally again?

Thanks.