Do not switch it off or do not change a SIM card, most likely, after some time the owner of this phone will call on it and you will be able to agree about the return.
If there was not a call or the phone is discharged, register IMEI or a serial number in the database of lost devices LoSToleN with the mark “Found”. If an owner checks it on this site, he will be able to contact you via e-mail.
