I have been trying to determine if a flow or trigger could help me wuth updating an existing case via web to case.  I have created a text field for adding an existing case number in my web to case page.  Is this possible?

Hello, I am trying to use a trigger to check or validate information in a Case custom field.   I have a list of data(serial numbers), I want to see if a serial number entered into my custom serial number field in the list of serial number i have.  If it is in the list, I want a notifiaction that it is on the list.   I was told a trigger may help me with this.  Can someone point me in the right direction?

Hello, I am trying to use a trigger to check or validate information in a Case custom field.   I have a list of data(serial numbers), I want to see if a serial number entered into my custom serial number field in the list of serial number i have.  If it is in the list, I want a notifiaction that it is on the list.   I was told a trigger may help me with this.  Can someone point me in the right direction?