Write on the boot folder of the SD card a file _wpasupplicant.conf with following content.
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=«your_ISO-3166-1_two-letter_country_code»
network={
ssid="«your_SSID»"
psk="«your_PSK»"
key_mgmt=WPA-PSK
}Replace _«yourSSID» with your SSID Replace _«yourPSK» with your Wlan Password Replace _«your_ISO-3166-1_two-letter_countrycode» with your country code, for example DE for Germany