There are times when a call is in order to a previous customer, but the question seems to be, "What do I need to say to the customer?" A lot of times, a renewal call is treated like a normal touching base call to keep your name in front of the customer. That is not the case.
The reason for a renewal call is to get them back in the store and get them thinking about a new vehicle. There are a few steps to do to make it an effective call to the customer.
Look at the previous deal. Most CRM tools will store all of the pertinant information in the system and you should know if they bought or leased, what their payment is, and maturity dates.
Maybe do an online evaluation of their vehicle to see if they may be in an equity situation. We all need nice trades and they are the best source to get them.
Check notes and history with the customer. Make small talk before going for the appointment. This goes back to making great notes in the system so you can refer back to them down the road. If their son is playing soccer, make a note of it and when you call them, you can say, "Is johnny still playing soccer?" This will make you stand out from the other salesmen.
Check inventory to see if you have something like what they bought from you last time or even a possible upgrade where you think you can keep their payment close to what they are paying now.
After this quick evaluation, call them. The number one goal is to get them in to discuss options with them. Once you get them in, go from step one of the sales process and qualify them in what they may want or need and go from there. Get these calls done early in the month as people do tend to get busier as the month goes on.