Change new document name

I work for a MSP and we have a customer who is wanting me to update their Sharepoint site. They have a library, and when they create a new document in that library it is automatically name '2017XXXX' where the X's are sequential numbers. They want this to be updated to be '2018XXXX'. They create these documents with a Form. I have tried to open and edit the Form and the column Name in Sharepoint Designer, but I have not had any luck. I do not have any experience with Sharepoint. Please help!