You need to export ProcessConfiguration.xml file with the command below:
witadmin exportprocessconfig /collection:http://TFS2017:8080/tfs/DefaultCollection /p:teamProject /f:ProcessConfiguration.xml
And add <State type="InProgress" value="Approved" />
in Feature's portfolioBacklog. Check below for detailed inforamtion:
<PortfolioBacklog category="Microsoft.FeatureCategory" parent="Microsoft.EpicCategory" pluralName="Features" singularName="Feature" workItemCountLimit="1000">
<AddPanel>
<Fields>
<Field refname="System.Title" />
</Fields>
</AddPanel>
<Columns>
<Column width="100" refname="System.WorkItemType" />
<Column width="400" refname="System.Title" />
<Column width="100" refname="System.State" />
<Column width="50" refname="Microsoft.VSTS.Scheduling.Effort" />
<Column width="50" refname="Microsoft.VSTS.Common.BusinessValue" />
<Column width="100" refname="Microsoft.VSTS.Common.ValueArea" />
<Column width="200" refname="System.Tags" />
</Columns>
<States>
<State type="Proposed" value="New" />
<State type="InProgress" value="In Progress" />
<State type="InProgress" value="Approved" />
<State type="Complete" value="Done" />
</States>
</PortfolioBacklog>
Then, import ProcessConfiguration.xml file with the command below:
witadmin importprocessconfig /collection:http://TFS2017:8080/tfs/DefaultCollection /p:teamProject /f:ProcessConfiguration.xml
In this way, you'll see the new state: