Question

He did not rehearse his dialogues properly.
He fumbled on the stage.(so) change in conjunction​

Answer 1

$\huge\red{Hey Mate}$

Conjunctions are the words which join two sentences together.

So your answer is

He did not rehearse his dialogues properly so he fumbled on the stage .

(Well meaning of fumble is to hold something or rub something when you are nervous )

Hope this Helped ...