Programming with database triggers

I am building a fault reporting system where by a problem reported is entered in an oracle database with a field that stores the levels of escalation (1,2,3). A new problem would be at level 1 after 3 days I want the level to escalate to 2 and after another three days the level would move to 3 . How can this be implemented to automatically take place. Can someone please show me how to code may be a databse trigger for the solution?

Please help