Great question, Isaiah. I haven't made this exact career move, but one recommendation that I would suggest is to work on side projects so you can gain experience building full-stack apps. Whereas your front-end projects likely used existing APIs as their data source, you would now want to focus on building an API yourself. You might even create a fork of one of your current projects that uses a custom backend instead of the current API it is using. Feel free to start with free or very cheap tutorials online (Youtube, Udacity, Udemy) to get you started.
To give you an idea of the type of side project I'm talking about, one full-stack project that I worked on in the past is a textbook exchange website. A friend and I built a website (front-end using React, backend using PHP/Laravel) where students could list textbooks that they wanted to sell, browse the available textbooks, and connect with sellers of the textbooks they wanted to buy. I started by building the front-end and using the Google Books API, since my friend was building out a backend at the same time. Then over time, the plan was to integrate with our custom backend and use our own library of books (using fake data in the beginning, until we launched).
Hope this helps provide some ideas and inspiration! Best of luck.