What a lot of people forget is that naptime is really rest time and about having a break from the bustle of activity. That means the child stays in the designated place for the entire rest time whether they sleep or not. Over time they will get the hint that you are not coming back until a set time no matter how loudly they protest. Some will just sit and play and others will actually sleep. Limit nap to an hour or in this case maybe 45 minutes but do several nap periods over the day. ie shorter but more often. This is also done to teach the concept of you stay here and I come back later. The nap periods should get longer and more productive meaning you can cut it back to two regular ones. Learning to self-soothe isn't something you can teach other than giving them the time to figure it out for themselves. Going into the room frequently to try and settle the child defeats the purpose because all it does is teach the child to be dependent on you to come and rub their back rather than on the child learning what works for them, hugging the blanket, chewing the corner, sucking their thumb, whatever.