To do this, navigate to your company setting and open the reminders tab. From here, scroll down the to file expiry section and click + add reminder.
Here, you can select who should receive an e-mail and dashboard notification and how long before the file's expiry date they receive it.
Once you are happy with the options you have selected, click add reminder.
You can set as many reminders leading up to the expiry of a file as you want.
To delete a file expiry notification, click on the red x next to the notification you wish to remove.