How to reduce VOC of solar panels to match the MPPT
Your question does not make sense without extra information.  

Why do you want to connect them in series?
Series connection only works properly if all are close to the same current rating. 

Why do you want to purposefully waste energy?
What is the voltage range that your MPPT controller WILL tolerate.

Tell us : Voltage and current of each panel under optimum load.
 Characteristics of MPPT controller.
 Load = ?
Why did you want to connect them in series. 

Are the panels identical- if so they could be placed in parallel with diodes to share the load.

Even if not identical in Wattage, as long as they have the same nominal Voltage you can parallel them with diodes for isolation and probably have it worK OK. A lower wattage panel will load down quicker and so a larger wattage panel will then contribute more.