He can not do anything at this stage. The process needs to take it course.
Assuming he denies it, that is all he needs to do.
There is nothing else he can do.
The Police will investigate and then make a decision.
If it shows there has been communication and she has not asked him to stop - then it is not harassment.
The Police would take no further action. The Police have to show she asked him to stop and he continued.
Even then, it's likely he would just get a warning to stop. It is only if there is threat of violence would they prosecute,
But there is nothing he can do at the moment - the investigation process just takes time.
I am sorry if this is not the answer you want, nor the one I want to give you, but I have a duty to be honest.
Can I clarify anything for you about this today please?