Google problem

I searched forums for this topic several times: Please forgive me if solution is already published!

I volunteer for a nonprofit organization, updating annual post of summer camps.

Updated page is:
/2020/01/04/summer-camps

But google is still showing previous post:
/2019/12/31/summer-camps

This is fixed by changing the publication date back to 12/31, what should i do for true date to be reflected on Google??

The page I need help with: [log in to see the link]