I lost my iPhone, can I lock it with the serial number?
I lost my iPhone and I found it off-line in the Find my app and I want to block it but I can't can you please block it by the serie number
[Re-Titled by Moderator]
For what to do next, see the section “If your iPhone or iPad is lost permanently or was stolen“ here:
… Find your lost iPhone or iPad with Find My - Apple Support
Might also want to mark it as lost, as described there.