Grab from all days
You can use the Grab tab to create an email, SMS or letter campaign in Applicant Open Days. Click onto the 'Grab' tab and select the criteria by which you want to filter students by. For example, if you only wanted to 'Grab' students who are Booked for a specific open day for a specific course, just filter by those conditions.
From this point you can then create your ad-hoc as normal.
Take a look at this link if you want to create an email ad-hoc
Take a look at this link if you want to create a CSV download