1.  Here is Section 2202(a)(5) of Cares Act:

(5) Income inclusion spread over 3-year period.--
(A)   In general.--In the case of any coronavirus-related distribution, unless the taxpayer elects not to have this paragraph apply for any taxable year, any amount required to be included in gross income for such taxable year shall be so included ratably over the 3-taxable-year period beginning with such taxable year.

Taxpayers don't ELECT to have the coronavirus-related distribution taxed over three years.   It's the default tax treatment.

2.  The coronavirus-related distributions were reported on Form 8915-E.  The 1/3 for 2021 is to be reported on 8915F which (as you indicated) is not final yet.

Why do you have to search for clients who had 1099-R for 2020?  Folks didn't just divide the 1099-R amounts by three to report the Coronavirus-related distributions.  Why not search for clients who filed Form 8915-E for 2020?  (Lacerte has the capability to display the filing of specified forms, including 8915-E.  I don't know about Pro-series Pro.)