The connecting word **Then** connects the action (the Israelites arriving safely on the other side of the Sea) with God’s instructions to Moses to close the path through the sea. (See: [[rc://en/ta/man/translate/grammar-connect-time-sequential]])
This could be translated as: “covered the place again where the path had been,” or “filled the whole sea again” or “went back to where it was before God separated it.”