How do you mention relocation in a cover letter?

I’m looking to move to a bigger city for no reason but to have better opportunity and friends in the bigger city. I’m looking to move to Nashville or Atlanta both about 4 hours away from where I currently live. I feel like me not living in those cities when I apply is the reason I haven’t had many interviews. I was wondering how to you go about mentioning your willingness to relocate and where in the cover letter do you mention it at the end or up front? I see most relocation have a reason like family or wife received a new job but I don’t have a great reason like that just that there is more opportunity there than where I currently live.

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