How to set back date used in form for one month

0

Hello,

I have some date set on forms. Need to find any solution to have that date - 1 month
for example:
Date on form is (YYYY-MM-DD):
1. 2022-05-05
2. 2022-01-10
3. 2021-12-25

Date that I expect need(YYYY-MM-DD):
1. 2022-04-05
2. 2021-12-10
3. 2021-11-25

Do you have any idea to solve it?

My poor trying on the screen below (a lot of counting and IF's and still get wrong format of the MM).

Thanks in advance for any suggestions and ideas.