Hi Abanoub,
I would glad to help. In storyline 3, I believe the feature "text to speech" is not available as it is exclusive to Storyline 360; but you may try to open a Storyline 360 with text to speech narration and it will work in Storyline 3. I think you can utilize the built in text to speech feature of Windows however this is kind of done manually since you still have to transcribe the text in Storyline 3 and upload an audio of the dictation there as well.
You may want to check the compatibility of storyline 3 and 360 here: https://articulate.com/support/article/Compatibility-Between-Storyline-360-and-Storyline-3-Project-Files
and if just in case, you intend to try the Storyline 360 trial pack you may want to see how the to speech is done through this link: https://community.articulate.com/series/articulate-storyline-360/articles/storyline-360-user-guide-how-to-convert-text-to-speech
