My 2 cents, I make chapatis daily at home to help my mother (mostly dinner).
1. Turn ON the pan(tawa) on high flame and let it be hot, place hand over the pan (don't touch it) until you feel the heat
2. Place your rolled chapati on the pan and let it cook on high or medium doesn't matter but enough so that some parts are bubbling
3. Flip the chapati and let it cook from other side, same thing let it bubble
4. Remove the Pan, make sure the stove is on High flame and place chapati directly on the Gas stove with a Roti tong and it will puff up then flip it and do same on other side
5. Your chapati is ready.
Note: You will not get this right in first time, it is same as rolling a round chapati. It takes time took me like 2 weeks to learn to roll the chapati and takes time to cook it perfectly as well so be patient