en_tn/exo/09/35.md

The heart of Pharaoh was hardened

Here "heart" refers to Pharaoh. His stubborn attitude is spoken of as if his heart was hard. See how you translated this in Exodus 7:13. Alternate translation: "Pharaoh became more defiant" (See: rc://en/ta/man/translate/figs-synecdoche and rc://en/ta/man/translate/figs-metaphor)

just as Yahweh had spoken by the hand of Moses

Here "the hand of Moses" is a metonym for Moses's activity in speaking. Yahweh had told Moses that Pharaoh would not let the people go, and Moses repeated it. Alternate translation: "just had Yahweh had said through Moses" or "just as Yahweh had said through Moses that Pharaoh would do" (See: rc://en/ta/man/translate/figs-metonym)