If your Betta doesn't seem stressed with the temps I wouldn't worry too much about it. Mine get well over 100F during the heat of the day and it never seems to bother the Bettas or spawning, eggs, fry etc.....The temp usually will go down into the low 90'sF and in some cases into the upper 60's F when it rains without any problems.
If the Betta is showing some stress related to the high temp-What I would recommend-Remove the heater, remove the hood and lower the water level-if you have a filter-lower the water just enough so the filter will still work-moving the water can help cool it off. You can buy those small personal fans that hang on your neck that run on batteries and use on the tank-I have seen some that have clips on them to use in a car that would be perfect for aquarium. Point the fan so the air goes across the water. Keep the lights off too.
If its an emergency and the Betta is in a great deal of distress...Lower the water level, turn off the filter, heater and lights and add an Ice bag to the tank-
Monitor the temp to make sure it doesn't drop too fast-yet fast enough to save the Betta. Keep a close eye on the Betta while you are using the ice bag method.
*If you have treated city water-I would add a drop or two of dechlorinater to the ice bag to be on the safe side-
*Don't ADD Ice directly to the tank-this can be harmful to the fish in more ways than one.....