I don't known which of the following I should use, because it translates with the same words.
It was explained to him that nothing else could be done!
It has been explained to him that nothing else could be done!
The present perfect 'has been' has a present significance, the use would be related to the present situation or discussion in some way, affecting it. The simple past would suggest there's not necessarily a connection to the present in any way- the time and the situation are over.