Sforno on Exodus 7:6/ספורנו על שמות ז׳:ו׳

1ויעש משה ואהרן כאשר צוה ה' אותם, after every instruction from G’d they followed the same procedure. Moses used to announce beforehand what would happen, seeing that he was G’d’s emissary. After that Aaron would translate what Moses had said into diplomatic language.

2כן עשו, they would do exactly this, not adding or subtracting anything of their own.