Hello,
Thanks for posting your query.
Presence of blue spot on the back is a harmless finding. These are skin tags or abnormal skin pigmentation spots which are benign in nature and remain like that for many years.
If you are too much concerned about its presence then you can get it removed either surgically or with the help of laser treatment but that is not necessary.
You only need to self monitor it for any change in shape, size, color, irregular margins, ulceration, pain, etc. If any of these changes do appear it means they need to be investigated and then removed under the guidance of your dermatologist.
So, please do keep a close watch on the moles on your body for change as such:

A- Asymmetry (irregular shape)
B- Change in the border of the mole (expanding in size or not)
C- Change in colour
D- Diameter (More than 6mm diameter is suspicious)
Removal of mole can be done either by surgical excision where local anaesthesia will be given by a thin needle surrounding the mole, which feels like a small pinch but the procedure of removal will be painless. After the procedure, dressing and antibiotics will be administered and after a week or two you should be fine. Also new methods like Laser removal can be done. Do discuss with the Cosmetic surgeon in this regard.

Avoid sun exposure as much as possible. Wear sun screen to reduce the harmful effect of UV rays on the skin which can aggravate the danger of mole turning malignant. Eat plenty of fresh fruits and XXXXXXX leafy vegetables to ensure good supply of vitamins and minerals for skin and antioxidant effect as well. Drink plenty of water.

Hope this answers your query. I will be glad to answer the follow up queries that you have.
Please accept my answer in case you do not have further queries.
Wishing you good health.
Regards.
Dr. Rakhi Tayal.

---