To group modalities of a categorical variable together: 

  1. In Multivariate analysis, choose the variable to explain and the explanatory variables.
  2. Click on the "+" button of the explanatory variable you want to group.
  3. Choose the new distribution you want for the modalities. If you choose to ignore a modality, the observations concerned will be removed from the model (you will loose statistical power). 
  4. Click on "Confirm" to validate your choice, click on "Remove mapping" to reintegrate modalities as they were initially.