Hi Kevin
Once having clicked on the page of the museum there should be a button just below the telephone number and the actions (call, save, etc.) where you should be able to submit any changes or problems.
After clicking on the button you might have to scroll down a bit to find the schedule again. Now you should be able to submit changes. It will however take some time to adapt because the change will be reviewed.
I hope my answer was able to help you!
Luca