Put the earbuds back into the charging case and then take them out again.
The earbuds will turn on and both earbuds automatically connect. The indicators display as shown below.
Power on: Blue
Lights up for 1 sec
Earbuds (L) and (R) are now connected: Purple
Lights up for 5 sec
The indicators may flash blue for a while after you remove the earbuds from the charging case.
The signal may not be coming in clearly, making the connection unstable.
Move away from wireless devices such as access points, or appliances that produce electromagnetic waves such as microwave ovens. After placing both earbuds into the charging case, take them out again.
You may be using a smartphone app that generates sound from only one channel.
Check whether you can hear sound coming from both left and right channels by playing back sound from a different app.