First solder the LCD connector J6 as it is delicate. Make sure to keep the soldering iron as far away as possible from the connector plastic body, as it melts very easily.

Second, solder the audio amplifier chip U1 as it is rather difficult to solder too: it is a QFN10 package with a special footprint that should make things easier by using the capillarity effect

We recommend to solder the speaker SP1, directly onto the PCB.

All remaining small components can be soldered in no particular order, as well as all the switches and connectors

Test everything without soldering the LicheePi Zero board first

On the LicheePi Zero board itself, unsolder the 3 small resistors near the RGB LED

Solder the LicheePi Zero board onto the main board

Solder the battery to the 2 corresponding through-holes, make sure that the polarity is correct