Question

He said he has regretted that he had acted so hastily

Answer 1

He said "I have regretted that I had acted so hastily.

Answer 2

This sentence can be converted to simple sentence if u like:

He expressed that he had been acting very hastily.

or u can convert it into direct speech if that's what u want:

'I regretted that I had acted so hastily'.

Hope this will help u out pal :)