You will have to run a script against the database to perform this, make sure to have taken a restorable backup and run the script against a test database before running the below.
I wouldn't suggest setting the incident number back to 0 unless you have cleared all incident data from the system. Setting to 0 with existing incidents may even end up in a sever corruption of your database.
The script to run is DBCC CHECKIDENT ('im_incident', RESEED, xxxxxxx)
Replace the xxxxxxx with the number you wish it to use.
You can replace im_incident with whichever module your wanting to reset so for Change - cm_change for Problem - pr_problem.
Thanks a lot. It works perfectly.