My phone was in water yesterday for 5 mins. Now it’s saying I don’t have a SIM card

This could have been caused by the water damage, firstly follow the steps at If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

If those fail, you will need to contact Apple support.

As this is accidental damage, it is unlikely to be covered by your consumer warranty.

Water damage is not covered by any warranty.