form 5695 take 30% for 2020,Safe Harbor payment in 2019

I paid more than 5% of my Solar Electric PV installation in 2019 so that I could claim the 30% rebate when my system was completely installed in 2020.  How do I change the percentage listed on IRS Form 5695; Line 6 from 26% to 30% to address that and what documents do I need to include in filing?