In general, the LCD display of a Polder thermometer can't be repaired once it's broken. If the LCD display is damaged or not functioning properly, it will need to be replaced with a new one.
Fortunately, many Polder thermometers have replaceable probes, which means that you may only need to replace the probe, rather than the entire thermometer. However, if the issue is with the display itself, then it will need to be replaced.
If the thermometer is still under warranty, you may be able to get a replacement from the manufacturer. You can check the warranty information that came with the thermometer or contact the manufacturer directly to inquire about the warranty coverage.
If the thermometer is not under warranty, you can try contacting a local electronics repair shop to see if they can replace the display for you. However, keep in mind that the cost of the repair may not be worth it, especially if the thermometer is an older model or if the cost of the repair is close to the cost of a new thermometer.
Overall, if the LCD display of a Polder thermometer is broken or not functioning properly, it's generally not repairable and will need to be replaced with a new one.