Use the following from an Elevated Powershell Prompt to force an AD sync to your O365 admin portal. You will be performing this on the server where Azure AD Sync is installed. When running this command you will need to wait 5 minutes before checking your portal to verify it is working. In larger environments this can take a longer time.
Import-Module “C:\Program Files\Microsoft Azure AD Sync\Bin\ADSync\ADSync.psd1”
Start-ADSyncSyncCycle -PolicyType Delta
Let me know in the comments below if you have any issues or this solution doesn’t work for you.