There are essentially two steps to using the system:
Step 1. Ensure that the document is available to DAS
Request the Office of First Filing to deposit a copy of the earlier application to DAS.
The exact means of doing this will depend on the requirements of the particular Office with which the earlier application is/was filed. See the DAS home page at https://www.wipo.int/das/en/ and the PCT Applicant’s Guide, Annex B https://www.wipo.int/pct/en/appguide/index.jsp for the procedure to be followed at each DAS depositing Office, or contact that Office directly.
Links to detailed instructions provided by each Office can be found on the DAS website at:
https://www.wipo.int/das/en/participating_offices.html
To make an earlier PCT application filed at WIPO’s receiving Office RO/IB available to DAS, refer to a separate User Guide “PCT and DAS”, available at https://www.wipo.int/das/en/documentation.html
Following your request to the Office, you will either receive an access code, or else a code which was given to you as part of the application process (for example, in the case of a USPTO application, the 4-digit confirmation number indicated on the original filing receipt) will become available for use as a DAS access code.
Step 2. Ask the Office of Second Filing to retrieve the document
The Office of Second Filing will retrieve the priority document from DAS only if you specifically request them to and indicate the access code on the application form.