[URGENT] seo onpage and fix html code to my blogger

I need seo onpage to my website..
http://Www.jokmobilmurah.com

Recently, I've read some tips from mybloggertricks. Which is missing h1 tags.. and I applied that tricks to my blogger.. and my traffics, and serp posisitio go down and my pageview as well..

I confused.
Can someone fix it for me?
Not just only fix it. I want to optimize my website seo onpage or offpage too..

Thanks

https://www.blackhatworld.com/seo/urgent-seo-onpage-and-fix-html-code-to-my-blogger.959854/

https://www.blackhatworld.com/seo/urgent-seo-onpage-and-fix-html-code-to-my-blogger.959856/

One thread should be enough @kadutz

Got the same problem thanks for the link @Finn