You can't. Everyone has pain tolerance for a reason. For instance, if you didn't have pain tolerance, you could touch a hot burner on a stove, and not realize you were hurting yourself. In the situation of a tattoo, if you want one, just man-up and get one. It's not like someone's cutting off your limbs or anything. Yes they hurt, but it's not a permanent pain.
Many psychological features, if not all, have an interesting property; that if you want to develop them, you just have to behave as if you already have them. For instance, if you wanna be patient, you just have to BE patient. Nobody can give it to you from outside. After a while you'll be patient, without suffering. It is the same for pain, if you can tolerate it, you will get used to it.