Introduction
In some cases, the categories in a demographic question are more detailed than the ones you wish to use for weighting. An example is a question about the respondent's Age which stores the age in categories of five years (e.g. 19 to 14, 25 to 29, etc), but where the data needs to be weighted according to more granular 10-year groups (eg 19 to 29, etc).
Method
When this is required you follow the normal process for creating a weight and drag and drop to merge together the categories in the table of targets.
See Also
How to Use Frequency Weights in Q
How To Create Expansion Weights