How can I increase DA?

Get high DA links to your website and that should increase your DA. But why are you only looking at DA. Concentrate on your onpage SEO specifically internal linking structure and once that is in place go and get high quality backlinks to your website.

Try to get good quality links from high authority sites to improve your DA. Since your site is just 2 months you have to wait patiently and also update your unique content with good keywords which will also helps to gain more.