List instances by running a SQL Server Discovery Report. That can be produced in SQL Server Installation Center -> Tools -> Installed SQL Server features discovery report.

In the folder where the report is created there is a Datastore folder. In that folder there is a file name Datastore_Discovery.xml. Edit that xml file and search for the "inactive" instance name. After where that is located there should be a ProductCode string. Copy the ProductCode string and paste it into the following uninstall string.

msiexec /x {51574D2C-DE28-4441-BDC2-967F0FFC0918}

There may be a few ProductCodes depending on how many components need to be uninstalled.