Not sure what you mean by field.  You do not need to create a field (like in Vendor; Other Info, you just create a reminder similar to a Task in Outlook.

It might be a little different in Enterprise, but in Desktop you can get to the Reminders from either the Company drop-down menu or there is a little clock in the upper right corner (which may have a number next to it if you have bill reminders, etc.  (Same place you see upcoming bills to pay.)

With the Reminders window open in the upper right corner there is a + to add new reminders.  In this case we're talking about a Task, Priority can be whatever you want.  Pick a date (time would be if you scheduled a Call, etc.) and put the info in Details something like:  XYZ insurance expires 02/28/19

You'll see the the option by clicking the With box to tie it to a Vendor, but I've never bothered using it.  It may be different in Enterprise, but it doesn't show up that you have a task pending when you're viewing the Vendor or paying bills.  So it was just one more step I never saw an advantage to using.   The task popping up was good enough for me.

and put the info in Details something like:  XYZ insurance expires 02/28/19