As long as you still see the angel tama you can hold down the far left and the far right buttons and a new egg should appear. Or you can push the reset button on the back GENTLY by using a pencil or toothpick. Press the middle button and choose RESET.
Set the date, time, and your birthday. If it's a V3 create a username. Then the egg will wiggle for a few minutes. Then it will hatch and you will see what gender of baby you have. Name the baby and start caring for it and you will have your tamagotchi working again!
GotchiGirl96