Your first step will be to contact a UPV professor who will supervise your doctoral stay at this university. You can find the list of professors for each program in this link (Information available for each program in the section “Organization of the Doctoral Program”-“Research teams”).
This teacher will be in charge of sending you a letter of invitation and signing the documents you need.
Once at UPV, the administration office of your supervisor’s department will provide you with the permissions for UPV services.
If you are applying for an ERASMUS grant at your home university, contact with erasmus_doctorado@upv.es.