To get the surrogate key in case of Type I SCD, you use a Database lookup step. The following image shows you an example.
In this case, the step is used to get the surrogate key for the REGION dimension:
In the upper grid, you look for the business key. As Table field, you put the dimension field that contains the business key, and as Field1, you put the field coming from your source data.
In the lower grid, you get the surrogate key and rename it with the name of the field in the fact table that you will populate. If the key is not found, you should use ...