Hi @Pugwash63
Unfortunately the phones software and hardware won't allow you to change from a single SIM to a hybrid duos type phone.
You'd need to return / sell that model and buy the specific model variant allowing two SIM cards.
Daily Driver > Samsung Galaxy s²³ Ultra 512Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
