Visual Studio - C# Code

Our lot numbers have a three digit auto sequential number on the tail end. The first letters represent the product, year and month. The 3 numbers represent the batch that was made that month. So, at the beginning of each month, we need to have an either automatic update that will know when it is the first day and first entry of the new month and roll the 3 digit code back to 000. Or if automatic is not feasible, a button that onclick will roll the number back to 000 but I would need an error message to populate at the first entry of the month. Any ideas for a code to achieve this goal? I am using Visual Studio and C#