So a project named "resources" is already present in your workspace.
But it is either closed, or doesn't have the "Servoy Resources Project" nature. If it would be a valid/open resources project it would show in the "Use existing resources project" section.
So your options are either to delete/rename the project named "resources" or to choose another name for your new resources project and select "Create new resources project" as you did before - type it in there.
But you said you want to use an existing one. So you have to see what's wrong with that project - if it's supposed to be a resources project; why doesn't it appear in the "existing" list?
See that it is open (have a look at it in "Navigator" view). If it is not open right-click -> "Open project". If you don't see it (I don't think that's the case here) - verify that it is on disk and then choose File -> Import Existing projects into workspace. In it you should see a ".project" file that contains these lines (among others):
- Code: Select all
<natures>
<nature>com.servoy.eclipse.core.ServoyResources</nature>
</natures>