Hi,
Dropdown can only be used when you have an attribute of type enumeration.
You should create an association between Location and another entity (Tool?).
When you create a new Tool, you can use a reference selector on this association to select the location.
https://docs.mendix.com/refguide/reference-selector
Also you don’t need to create an attibute for every location (in your example RW, VS, ...), but only 1 string attribute (e.g. Name) and you can add all different locations in the entity Location.
I would also recommend to go through the rapid developer course as it will help a lot of understanding the domain model and some widgets!