NOTE:
Existing companies that were converted from a prior version won't have the proper formulas for Super Catchup. To create the formulas in an existing company, you'll need to create the 401k settings in a brand-new company and copy over the formulas. Any new companies you create will have the updated formulas.
The instructions below are for 401(k), but they also apply to any other retirement benefits with a Super Catchup: 403(b), 457(b), Roth, SIMPLE, etc. Just select the appropriate retirement plan formula.