How can I write an external dashboard for an e-commerce app?

Hello everyone, currently I am building an e-commerce app as a mern-stack project. I finished the design part and the api. Now I want to build the dashboard, but I want to do that with an extra frontend, so that the employees can get logged in into this frontend to administrate the shop. So I need an information, how I can connect a second frontend to my backend. I taken a look at the tutorials on youtube, but there seems nothing to fit to my code. Thanks for any advice.