Add this repository through the Umbrel user interface as shown in the following demo:
umbrel-0.5.2.mp4
Alternatively, you can use the Umbrel CLI as described below.
To add an app store:
sudo ~/umbrel/scripts/repo add https://github.com/decred/umbrel-app-store/
sudo ~/umbrel/scripts/repo update
To install DCRDEX from the app store
sudo ~/umbrel/scripts/app install decred-dcrdex
To remove this app store:
sudo ~/umbrel/scripts/repo remove https://github.com/decred/umbrel-app-store/