All you need to do for now is to increase the amount you’re pledging in Kickstarter by the cost of the additional items you wish to buy. When the Kickstarter campaign ends, you'll be able to select your extra items using the pledge manager survey we’ll sent out.
The estimated shipping date is October 2018, but keep in mind this is only an estimate. We will keep our backers updated on any changes. Also, due to the logistics of international shipping, backers in some regions of the world may receive their rewards sooner than others.
Don't see the answer to your question? Ask the project creator directly.