There are online websites available such as udemy which offer online diploma in psychology courses. There are no such colleges/ universities which offer diploma in psychology courses in online mode. I am mentioning below the name of the colleges which offer diploma in psychology course at offline mode:

1. Jesus and Mary College New Delhi
2. Saint Xaviers College Mumbai
3. Presidency College Chennai
4. Christ University Bangalore
5. Sophia College Mumbai

Read more about Psychology courses by clicking on mentioned below link:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.careers360.com/courses/psychology-course&ved=2ahUKEwjLjJmvoc71AhXMsFYBHaFsBegQFnoECAUQAQ&usg=AOvVaw0mQrQmigxXxzmzT9WOyDj7