Macro to Compare Two sheets, if Match *within* Cell then Update another Cell

All,

I need to write a semi-complicated VB macro that accomplishes the following: It compares two worksheets (named CTP and SRTM). It uses comma separated entries in column B of the CTP sheet and attempts to find a corresponding match in column A of the SRTM sheet. If a match is found, it copies the corresponding entry in Column A of the CTP sheet to Column B of the SRTM sheet.

I know this may be hard to visualize so I uploaded a mock workbook and an example below to illustrate what needs to be done:

Example:
In the CTP Sheet, there are 2 columns. Column A contains a Test Step Number and Column B contains multiple comma separated Control IDs. The first Cell with Control ID entries contains: "IA.2.a, IA.2.b, IA.4.4, PL.2.1". The macro will first take "IA.2.a" and search through column A of the SRTM sheet for a match. If a match is found it will then populate Column B (the Test Step Number) with Column A of the original CTP sheet that had the Test Step Number. So in this case, the number '4' would be copied from the Column A of the CTP sheet into Column B of the SRTM sheet (next to the IA.2.a entry).

If there's any additional information I can provide I'd be happy to do so. I appreciate it if anyone could provide some general guidelines as I'm relatively new to VB.

Thanks.