Need a error fixed for a Java Spring Boot/MYSQL web project.

I am working on a form for a project and I need help fixing a validation error. I want a validation error message added if a user tries to register with a email that is already registered. Need someone who is good with JAVA Spring Boot/ MYSQL.
attached is the project. You will need to create a new schema in MYSQL workbench and update your applications.properties file to test the project. I attached the error that i am recieving when trying to enter a email that already exists in the MYSQL database