Hi,
Have you inserted the SIM in the correct way? Here's a link that shows how to insert your SIM card.
https://www.youtube.com/watch?v=rmo1HPmWDvc
If it is in the correct way, try inserting it into another phone to prove that it works i.e. phone will detect SIM card. Also try another SIM card in your phone to prove that the SIM card reader in your phone works.
If it does work in another phone and another SIM card does not work in your phone the SIM card reader may be faulty and needs to be replaced.
Since it is soldered onto the circuitboard, suggest you contact a professional mobile phone repair service.