It's your homework, I will not give you exact answer.
From your code I can see that you have not properly understand your assignment.
First focus on the requirement.
1. implement constructor. That you have done, it
2. implement updateTemp; you have not. When you implement a member function you need to follow this simple rule. Follow this guide C++ Class Member Functions
You still have issue understanding requirement of updateTemp; Your assignment suggested a specific requirement. You need to follow that. "
The updateTemp function takes a new data value and determines if one of the temperature values in the object should be updated
". Focus on this.
3. Implement access function. in the class declaration no argument is set, but your definition shows argument. And what would you do with those argument? Seems nothing.