I got a tattoo without knowing it is Harm, Do I keep it or take it off?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

‘Abdullah ibn Mas’ood narrated: “Allah curses those ladies who practice tattooing and those who get themselves tattooed, and those ladies who remove the hair from their faces and those who make artificial spaces between their teeth in order to look more beautiful whereby they change Allah's creation”. His saying reached a lady from Bani Asad called Umm Ya’qoob who came (to ‘Abdullah) and said: “I have come to know that you have cursed such-and-such (ladies)?” He replied: “Why should I not curse these whom the Prophet has cursed and who are (cursed) in Allah's Book!” [Al-Bukhari and Muslim]

This is a sound evidence that tattooing in all its forms is a major sin. Any woman who practices tattooing or gets herself tattooed faces great dangers and will be punished severely on The Day of Judgement.

So, one should repent immediately and remove any such things if possible; i.e., if this will not cause any harm to them.
Imam An-Nawawi said: “Our companions said: “If it can be removed by treatment, it must be removed. But if it requires an operation which might cause the deterioration of an organ by losing it completely or partially, or create a major problem (injury, pain, wound), then it could be left as Allah does not cause any hardship for this Ummah (nation).”

But if one (a man and woman) delays removing the tattoo deliberately, he commits a sin.

For more benefit on tattoos and tattooing, please refer to Fataawa 89609, 104893, 266893, 85613, 89503, 84503 and 84562.

Allah knows best.