To convert a text string into a cell reference in Excel:

1. Create the text string that represents the cell reference using the CONCATENATE function or the & operator.
   Example: =CONCATENATE("Sheet1!", "A1") or ="Sheet1!A1"
2. Use the INDIRECT function to convert the text string to a cell reference.
   Example: =INDIRECT(B1)

In your case, use the CONCATENATE function to create the text string that represents the cell reference you want to convert, and then use the INDIRECT function to convert it to a cell reference. You can then use this cell reference in your formulas to pull data from the appropriate sheet.