Please refer
SDDC Upgrade and Maintenance Document for viewing and scheduling upgrades
For requests regarding SDDC upgrades/maintenance reschedule customers need to reach out to your TAM/VMware Representative who can file an internal request with the upgrade team to have it rescheduled on the basis of business reasons.
In case there is no TAM assigned to the organization then file a Support Request with GSS for VMware Cloud on AWS support to have upgrade/maintenance reschedule/postpone request fulfilled.