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.