Permalinks 301 Redirection not working

Hello,
My website is currently in this format : year/month/postnam.html and i need to change it to website/postname.
But when i change the perma links, i get not found error on old links, the plugin only works if add pages manually, is there any way to automatically pick all the 301 redirection after perma change ?

https://wordpress.org/plugins/redirection/