Triggers in MSSQL is a concept for a piece of code which executes when you have changed data in a table. Be that inserts or updates/ deletes, something can happen as a consequence of the operation on data. So you see you do not need a trigger.
What you need in MSSQL is a maintenance plan, if you set up a maintenance plan which executes a TSQL task, which then get all expired cources without expirery date set for instance and update those with today and send a mail.
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