Sim

[enajnollid]

Hi, please could anyone help? I have just purchased a Samsung s21 second hand from a friend. When I am inserting my sim card it isn't connecting and on the sim management it still says my friends number and not mine. Thank you 

[Glenntech]

Has the phone been factory reset?
If not then your friend will need to do this.
A factory reset will remove information and account data such as this

[jax57]

I think it hasn't been unlocked yet. So you can get a unlock code.

[AshtabS9Ultra]

Or to add to the above he may have an esim on the device that needs deleting