The mint is super-easy to divide. Dig it up, and cut or tear it apart. You need not be kind to it, because it will come back.

For the oregano, if it's spread so that it has multiple stems, you can do something similar, though I'd probably be somewhat kinder to it than with the mint.

As for the sage, you want to figure out whether you actually have more than one plant. If you do, you could divide them, but if you don't, you'd need to root new ones by layering or by taking cuttings.

Good luck!