how to increase authority

Check the backlink profile and disavow the links with a high spam score and non-quality links.
And get your backlinks from sites with High DA, it will increase your site DA.

I think it's not about the DA that affects your ranking. Do work hard on your Off-page SEO. Do guest post and backlinking to authority sites and other link building strategy. If you have new post, ping it. Also try linking your innerpages.