Copy formula result to text field (for public form)

I’ve created a dizzying array of lookups, rollups, and formulas to finally arrive at a result, which is in a formula field. I want to copy this text string result into a text field that can be displayed and edited on a public form (long text or short text). I know how to “pull” results into a new field using formulas, lookups, and rollups. But how do I assign a value to a text field that can be used in a public form? How do I “push” my result into the field? Thanks!