Hi Valentine @ValentineSokil ,
It looks like there is more wrong with your model, so it’s really best to start over (believe me, it’s counterintuitive, but absolutely worth it!).

But what you can do for the speaker, is make a connection (yellow line) between two Vertices with CTRL+J and then Delete all Vertices of the left Speaker nad Duplicate the right Speaker and move it in place and Fill the hole with two Faces, similar to the right side.