I had a pilonidal cyst removed about 9 years ago
I understand your concern. It seems you have a pilonidal sinus, which is a small hole or tunnel on the top of the bottom crack. This may be a residue of the cyst you had and, unless it gets infected, it is harmless and does not require treatment. You need to keep the are clear (shower regularly) and use lotion to avoid irritation and friction.
If it becomes painful, red and swollen you need to see a doctor for a drainage and antibiotic treatment.
I hope this answers your question. Let me know if I can assist you further.