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Page Templates
Unfortunately this options is only available in the premium version of this theme. ie. Blog Mantra ProFull Width page templates
For full width page templates, you can add new page and select full width page templates option from template dropdown list. If you still get confused then you can go through this link - https://codex.wordpress.org/Pages#Creating_Pages
Contact our Customer Support that is always ready to help you with any possible questions, problems or information.