Have you tried AMS Web Sign In yet? It will connect you with all your reviewer information and fill in parts of the submission page for you. If you are creating your AMS Account for the first time, be sure to add your reviewer number to your profile.

If you prefer to submit your review without signing in, you may do so by following the link below:

Interactive Web form

• You will be able to view and verify all information entered. 
• If the system is able to TeX your review text successfully, you will be able to see your review in PDF as it will appear to the editorial staff at Mathematical Reviews.  
• If the system is not able to TeX your review text successfully, the Mathematical Reviews staff will make the necessary corrections.