To add a bookmark to the 1inch iOS app internal browser, first navigate to the browser, then enter the URL of the site you would like to save.
Then when the page loads, tap the "star" icon in the top right corner of the screen.
That's it! You have now saved a bookmark, and it will now be visible on the main browser search screen.
To remove the bookmark, simply visit the page you want to remove, and deselect the star button in the top right corner. Your bookmark will then be removed.