iPhone is not recognizing sim

it says it cannot find the sim

Just out of the blue?

Try this:

Remove and reinsert the SIM card.

If it doesn't help contact your carrier, maybe the SIM card is damaged, ask for a replaced (new) card. Normally it is free.

Als ask to check if the SIM tray is bent, as even a tiny misalignment can cause the SIM card to not fully connect with the internal contacts in your iPhone.

See also ⤵️

If you see No Service, Searching, or SOS on your iPhone or iPad

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

How to unlock your iPhone for use with a different carrier

How to unlock your iPhone for use with a different carrier - Apple Support