There's 3 scenes related to the slime black thong scene
1-Putting it : Follow the trail of clothing from the blue dragon drake
2-Getting rid of it : Enter that special place with the weird floor symbol after the first green slime
3- Trying to escape : try to exit the area without getting rid ot the slime black thong ( go right until you see the exit of the forest )
There's also a walkthrought pinned on the Grove NSFW-General chat on the discord server