I inserted a new SIM card and now it is asking me for a PIN or unlock code to unlock it

There are several reasons why your device might be locked when you insert a new SIM card.

SIM Card Lock

A SIM card lock protects your SIM from being used on other mobile devices. Follow the below steps to find out how to lock or unlock your SIM card.

1 Go to "Settings".
Tap to enter Settings menu on a Galaxy S10
2 Tap "Biometrics and security".
Tap to enter the Biometrics and security menu on a Galaxy S10
3 Tap "Other security settings".
Tap to enter the Other security settings menu on a Galaxy S10
4 Tap "Set up SIM card lock"
Tap to Set up SIM card lock on a Galaxy S10
5 Tap "Lock SIM card".
Tap to Lock SIM card on a Galaxy S10
6 Enter your SIM card PIN, then tap "OK". The default PIN number is 1234.
Enter SIM PIN to unlock SIM card on a Galaxy S10
7 When the SIM card lock is activated, you can tap "Change SIM card PIN" to change to a new PIN number.
Tap the Change SIM card PIN on a Galaxy S10
8 To disable the SIM card lock, tap "Lock SIM card" again, then enter the PIN number.

Network Lock

If you originally received your device from one network provider and your new SIM card is from a different network, the original network provider may have locked the device to their network.

Samsung does not lock any of its devices to any particular network. You will need to contact the original service provider or retailer to request an unlock code.

Some service providers may allow you to unlock the device for a small charge or for free, whereas others may not allow the device to be unlocked at all.

Region Lock

Some Samsung smartphones work only with SIM cards issued from mobile networks from a certain region. This region should normally be found on your device's packaging when you purchase it. 

So for example, if you buy a smartphone in one country, it may not work if you try use it in a different country with a SIM card from that country.

If this happens, you will need to speak to Samsung Customer Services regarding unlocking the phone.

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