Which board are you using? BLE Nano or BLE Nano2?
The sketch is uploaded over DAPLink through the SWD interface, instead of the UART. If you keep pull the D5 to low during power up, the Nano will stay in the bootloader for OTA firmware update.
Regarding the map of the UART pins, try using the
Serial.begin(const uint32_t BaudRate, uint32_t rx_pin, uint32_t tx_pin).