OCD has been triggered or aggravated by many due to the COVID situation.
The psychiatrist can write a letter w/letter head and date, as an attachment, to the student. The student can then send this letter to the professor directly. The letter should state that the student is having increased difficulty and requires additional accommodations, opportunity to make up work, and extensions on assignments.
This letter could also be sent to the Office of Disabilities, dean, chair or provost as mentioned above but a family member who teaches at university tells me that they receive letters like this directly. In fact, letters are sometimes sent in situations where accommodations beyond those offered by the Office of Disabilities are needed, or when a student not registered with the Office of Disabilities has a problem (concussion, acute illness etc.) requiring temporary accommodations.
It is true that accommodations are at the discretion of the professor, but often a dean will tell the professor to accommodate.