Please first check whether the earphones are fully charged. The earphones will not switch on if their battery – or that of the charging case – is empty.
Charge the case to ensure the earphones can be charged while placed inside. Make sure they are correctly positioned in the case and that the charging contacts are clean.
If the earphones still do not turn on after charging, press and hold the multifunction button on the case for around 12 seconds to perform a manual reset.