To manually force a sync with a Wallet or Exchange Connection, simply tap on the double curved arrow to the left of the connection name. You can do this on the Connections page. To get there, go into Delta -> Settings -> Connections, or by pressing here.
You can sync all connections simultaneously by clicking "Sync all connections" at the bottom of the screen. Note that if you have multiple connections to the same exchange, this might cause you to get rate-limited. Please sync multiple connections to the same exchange separately and with some time between each sync to avoid being rate-limited.
PRO TIP: If the sync is failing to complete, please try again and do not go off of the connections page or lock the phone until the sync(s) have completed.
PRO TIP 2: If you are getting an error when syncing, you can take a look at this article here to help explain the issue.