Updating a field in a child record based on selecting parent summary value

If your user will need to edit a Ticket after selecting the Event and Date, I would suggest the following process:

1. User is presented with a report showing the Events/Date (just as it is now)
2. User selects the Event and is taken to the Event Form, showing a list of Registrations
3. User selects an Registration and is taken to the Registration Form, showing a list of Tickets
4. User selects the appropriate Ticket and makes the necessary update

Alternate Process:

1. On the user's Homepage, the user is presented with a Search Widget that searches the pertinent fields on the Tickets table
2. User selects the Search and enters the information on-hand for the specific Ticket Holder (Name, Phone, etc) 
3. User is presented with a listing of Tickets based on their search
4. User selects the appropriate Ticket and makes the necessary update