Make sure you mount the outdoor unit on the pole and insert new batteries. Then press reset on the outdoor unit.

If the LED lights up after a few seconds, you can try the following:

1: Place the outdoor unit without batteries in a dark room so that the solar cell can no longer produce any charging current.

2: After 24 hours, check whether the LED has gone out. 

3: If the LED has gone out, you can put the batteries back into the unit.

The LED will light up again briefly and then a bleep will be heard every 16 seconds.

4; Reconnect the indoor unit with the outdoor unit.

After this, the units should be connected again and the weather station can be used as usual.