Proper scraper and take as much as possible off
https://www.screwfix.com/p/heavy-du...VB7LtCh3IogoREAQYASABEgKgOfD_BwE&gclsrc=aw.ds
Then something like this for the remainder
https://www.screwfix.com/p/no-nonsense-sealant-remover-100ml/88987
Maybe try a heatgun
Wire brush and elbow grease will get the rest of it off.
Hopefully the 'black stuff' comes off just as wellI've got something similar on some of my rendered wall at the rear of the house where someone had a crap conservatory up. Albeit the stuff on my house is probably about ten years old so it simply comes off in chunks by hand cos its perished that much. Should really get round to peeling it all off! Looks like yours is coming away not too bad though.