There was a facility that was launched by EPFO while back where it was possible to link Aadhaar to UAN without logging in but it’s no longer available. To link Aadhaar with UAN, one should login into the UAN portal and then update the Aadhaar on the UAN portal. Once it’s updated it would be approved by your Employer and then it would be sent to field office for verification.
Field Office is the PF office which looks into your PF accounts. Once it’s verified from the field office the Aadhaar would be linked to the UAN number. You can see more about how to link UAN with Aadhaar over here – https://www.epfguide.com/link-aadhaar-to-uan-in-epfo-portal/
