You have to make a folder in your child theme. The folder must be named as Dokan. Now you have to insert the store.php file in this folder. In the theme function.php you have to register the sidebar. In the child theme folder you have to also insert the sidebar-store.php file. Then you have to change the style in your style.css file of your child theme. I have fixed your store page last day but it is very complicated to fix all the page because it is all about your theme. So many more customization will require for fixing your theme design. I have tried my best to help you .