I am in no way a medical professional and my reply is anecdotal
I've had a couple, and while I prob should have went to get professional attention I dealt with them. I basically just boiled some water and prepped a clean needle/knife point, not particularly sharp as I just want the point for leverage. Cleaned the foot and used the hot water extensively to soften the skin around the nail as much as possible... then I steeled myself for some pain and started to use the point to get just under the nail and start teasing it out and working towards the ingrown corner, often using my other hand to pull the corner skin of the toe clear as much as I can and even though it took quite a bit of force eventually it popped back out and I I was able to trim it normally and clean the wound, the majority of the pain eases at once as soon as the pressure is removed though and the wound has a chance to close.