Sometimes the scheduling interval doesn't quite give you the control you need. For instance, you might have bottles that need hydro tests each year over the following 5 years. This means you would need to manually set the date on each bottle depending on when it is next due.
This is where the override feature comes in. Make sure you have selected the Allow Personnel to set the date of the next item inspection option when setting up your inspection. So using the Hydro example you might have an inspection setup like this:
Once that is enabled you can go and find your inspection on any bottle and set the date there.