InfoPath Dev

I’m getting a 404 error on an old site. Instead having to rebuild a whole new form is there a way to upload an old form onto a new list site. I’ve tried but regularly get an error. And also the option to customize form is grayed out can only select use default form. Any assistance is greatly appreciated. Thanks

Is this a list or library form? If a list form, I think the only option would be to save the existing list as a template and then create a new list off if it. If a library form, you could just republish to a new library. In terms of the 404 error, you may want to take a look on the SharePoint Server for that?