Odd-even margin

You can do this with the inner and outer keys. The inner (outer) margin is the left (right) margin on odd pages and right (left) margin on even pages. Hence

\usepackage[top=2cm, bottom=2cm, outer=1cm, inner=2.1cm, headsep=14pt]{geometry}

should do what you want.

As mentioned in comments below, the twoside option must also be added, either to the documentclass or geometry. The book class has this by default, while report and article does not.