Try changing it on a store computer. Or use a different browser.
Not sure what week you are trying to change. But, I am sure you have to change it a week+ away from todays date. Just like asking for days off, you have to request a week+ ahead of time.
Oh im sorry i left out that im trying to do a "permanent schedule change" instead of just a temporary one for the week. Does this change anything?
No.
As was said, if logging out and back in doesn't fix it, try from a store computer. If it still doesn't work, talk to your schedule writer. We can specify your availability manually.