The Disability Resource Center can assist you with receiving accomodations for your block exams and shelf exams. Keep in mind, receiving accommodations for the pre-clerkship blocks does not necessarily mean you will receive accommodations for the Step exams.
Applying for USMLE accommodations can be a challenging process. In addition, it takes at least 60 business days for applications to be processed. The Office of Student Success encourages you to start early and work with your Learning Specialist throughout the process.
Resources
Bryan Little, a current 4th year, created this excellent presentation based on his experiences applying for accommodations: USMLE Accommodations Presentation
Unsure where to start? When to start? Please refer to this checklist: student_checklist_and_timeline_for_licensing_exam_accommodation_requests.docx
This Certificate of Prior Test Accommodations (CPTA) is for those students who currently have accommodations with the University. It is required for the USMLE application: 
usmle_certification_prior_accommodation.pdf
Websites
Check here for all and any updates to the accommodations process: https://www.usmle.org/step-exams/test-accommodations
The Disability Resource Center ensures accessibility and works to create a universally designed campus and reduce the need for individual accommodations through a proactive collaboration with the College of Medicine. This is where to start if you are seeking accommodations for the blocks: https://drc.arizona.edu/
The ABLE Clinic provides individuals with evaluations and testing to assist in diagnosis, treatment recommendations, and coordination of care: https://salt.arizona.edu/able