The registration process for Amazon's March 20th event is as follows:

Log in to the Seller Center: First, sellers need to log in to the Amazon Seller Center to ensure that they have a seller account and are eligible to participate in the event.

View the event page: On the homepage of the Seller Center, find the "Promotion" or "Event" tab and click to enter the event page.

Select the event type: On the event page, various types of events that can be registered will be displayed, such as special promotions, flash sales, coupons, etc. Sellers can choose the appropriate event type according to their products and needs.

Fill in the registration information: Click the selected event type to enter the event registration page. Sellers need to fill in the relevant event information, including product ASIN, event start and end time, discount range, etc.

Submit the registration: After filling in, click the "Submit" or "Register" button and wait for Amazon to review and confirm whether the event meets the requirements.

Please note that when registering for Amazon events, merchants must strictly abide by the relevant rules of the platform to ensure the quality of the registered products and provide accurate information. At the same time, merchants also need to abide by activity inventory restrictions, price restrictions and other rules to ensure the fairness of the activity and the interests of consumers. When participating in Amazon activities, merchants also need to maintain active communication and feedback with the platform to better understand the platform's requirements and suggestions, and optimize product information and pages to increase sales and word of mouth.

Please note that the specific registration steps and requirements may vary depending on Amazon's policies and activity types. Therefore, it is recommended to read Amazon's official guidelines and requirements carefully before registering to ensure that the registration process is completed correctly and effectively. If you have any questions or need further assistance, it is recommended to contact Amazon's customer service team.