Haaris:
Design and Reference within Platform Documentation is a great resource (Help at the top right of the application). I think reviewing Cube Integration and Data Sources will help you get to where you want to go with this.
Design and Reference > Cube > Cubes > Integration
For the Cube where you are importing this data, you would need to enable one of the Attribute dimensions. When a Dimension is Enabled, it will appear in the Stage area and data can be imported into it for a particular Scenario Type.
Design and Reference > Data Collection > Data Sources
For the data source assigned to the import, create Source Dimension for the enabled Attribute dimension then set the position where the dimension data will exist in source data.
Next time you import the data to stage, based on your data source configuration, data should map to newly enabled dimension.