trying to apply my branding to a template but I don't have the Design button

Had this exact same issue and cannot believe the answer is that they took it away in the new update. It's the only reason I chose to use Adobe 

Hi @Rubi267906352bye , thanks for your note! Adobe Express recently launched a new version, so the tutorials you're mainly seeing on the web may be different than latest update. One-click apply brand is on our teams radar, but in the meantime, you can access your brand colors through the color picker for individual objects. We are looking to make major improvements to the Design tool, but in the meantime, I'd invite you to upvote the feature on User Voice: https://adobeexpress.uservoice.com/forums/951181/suggestions/47159953. Thank you!