You can just wait for Disney to get to your reservation. They are working in a rolling process and should be to August in the next 10-14 days.
However you might be able to simply make a change within
MDE. Check your reservation and see if you have an enabled "Modify" button when you look at your resort details. If it is enabled then you might be able to simply reschedule to any available resort.
However if your August trip was originally at an early time and it was rescheduled / moved due to Covid-19 and you have a "Recovery 20" rate then you might need to call if you want to get your resort move completed before Disney gets to you or lose any discount(s) by using the "Modify" reservation process.
Here are some phone numbers to try:
407-934-7639 - Regular modification number from MDE ( Modify button is missing or not working for you)
(407)-560-2428 - A good reference from the Disney Chat tool.
(407)-939-1936 - general number
(407)-939-5277 - WDW Disney general reservation number
(407)-939-7866 - Guest Services call back number
Dave