The words are quite similar and can be used interchangeably. If you check in the dictionary they fall under ' synonyms' of each other. I was sent to go and assess the situation I was sent to evaluate the situation.

There is no difference. It really depends on how you use the word in a send. Overall, the meaning is the same.

The only possible shade of difference in their usage is that "assess" is used more often to describe analyzing a situation or action beforehand and "evaluate" is used more often to describe analyzing it afterwards. But they can each be used either way.