Change the narration: Hyder said, "I will manage hereafter."

Hyder said that he will manager hereafter.

Hyder said that he would manager hereafter.

Hyder said that he will manager thereafter.

None of these

"will" changes to "would" in reported speech.

"hereafter" changes to "thereafter".

Verb "manage" stays the same.

So the correct sentence: Hyder said that he would manage thereafter.