Translate Main navigation with WPML

Hello,

I just buy your theme for one of my client. I didn’t made his website but he person who did use your theme.
I am working for my client for the translation of his website.
This problem is : I don’t know how to translate the main navigation menu. Actually, I don’t even know how to edit the menu in the wordpress “basic” editor, not on the “live” editor.

Could you please give me a solution please ?

Thanks

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