1) Confirm that the charging case has power left (open the lid of the charging case to check if there is any indication on the LEDs).
2) Put the left earbud in the charging case and if the left LED flashes twice, that means the earbud is connected to the case. Similarly, when you place the right earbuds in the case, the right LED will flash twice when connected.
3) Close the lid after placing the earbuds in the charging case and start charging.