You need access you something when you need to assess it. For example, if you need to assess the locker of a rich man, you need to access it. Access is a way of approach, a method or reaching or entry.
Assess is to set an estimated value on property, etc. for taxation; estimate, appraise: “Income tax officials asses the properties of rich men.”
Excess, on the other hand, means when something surpasses a limit or is surplus. For example: The excess liquor he had at the party meant that he had a bad hangover the next day.
This is a good place to know the usage. Mostly we see when to use the word but here the usage of access and excess (not even on askanydifference) is given which means the actual and real life examples of the words.