It's possible to replace the SIM card connector, but need to be very professional because it's soldered on the motherboard and you need to disassemble the phone.
Before replace the SIM card connector, i suggest that
1. Clean the SIM card.
2. Try the SIM card in other phones to see if it's well.
3. Open the phone and clean the connector. Check if the pin of the connector is broken.
If all failed, you can consider to replace the connector.