How did Iblis entice Adam and Eve to eat from the tree so that they would be immortal, even though immortality was already theirs in Paradise?

The Paradise of Adam is the Eternal Paradise, by consensus of the Salaf of the Ummah. There is no contradiction between this and Satan's whispering to Adam about immortality, because Adam did not know it was the Eternal Paradise until after Iblis whispered to him. Alternatively, he knew it was the Eternal Paradise but thought it was possible to exit and then return to it. Or perhaps he knew it was the Eternal Paradise, but the reason for immortality was unknown to him, so Iblis whispered to him that eating from the tree was the cause of immortality. Or, he forgot the covenant of his Lord, and Satan made him forget it in a moment of heedlessness and forgetfulness.