How to insert 2 SIM cards?

you can't insert 2 sims.. you can insert 1 and then use esim

Using Dual SIM with an eSIM - Apple Support

or.. depending on where you purchased the phone, looks like certain ones can take 2 nano sims back to back..

Using Dual SIM with two nano-SIM cards - Apple Support

where a buy a new dual sim card tray? if i buy one my iphone will have the ability to use both cards?