You can reset both UNIT-4's and X02, and then re-pair.

Start by resetting each UNIT-4, one at a time:

• Turn on UNIT-4
• Set Mode to W+
• Hold the Mode button for around 10 seconds - the LEDs will flash fast a few times
• Turn off UNIT-4
• (Repeat on your second UNIT-4)

Then reset X02:

• Connect X02 to power/your device and wait for the LEDs to turn on
• Hold the button for around 10 seconds - the LEDs will turn off
• Disconnect X02

Then pair UNIT-4's to X02:

• Turn on both UNIT-4
• Set mode to W+
• They should be in pairing mode automatically - the LEDs will be flashing around 2x per second. If not, hold the Mode button for 2 seconds until the LEDs are flashing fast
• Connect X02
• UNIT-4 and X02 will connect automatically