A minor seventh chord includes the root, third, fifth, and minor seventh degrees of the scale. I assume you're referring to a minor/minor seventh, where the third degree of the scale is also minor. A minor seventh chord can be created in any key, but I'll give you a few examples.
In C, you would use C, E flat, G, and B flat.
In F, you would use F, A flat, C, and E flat
In G, you would use G, B flat, D, and F
This can be done with any note as the root. I hope that helps! Let me know if you need any more help with that. :)
