I want to amend my 2021 California state return - 2021 CA residency status from part-year resident to resident. Why do not I see the form changed from 540NR to 540?

Filing jointly - original filing had one part-year and one CA resident. During the amendment, I need to change it to both CA 2021 full residents (during amendment, the residents details entered for both the spouses are exactly same - CA full time residents). The original filing had 540NR form. After amendment, will not the form changed to 540?