Force-quit
Swipe up from the bottom and pause to bring up app switcher. Swipe Dilly off the top.
Reopen
Tap Dilly to relaunch. Most state issues clear on relaunch.
Update iOS and Dilly
Confirm both are current. Compatibility issues with very old iOS versions are the second most common cause.
Reinstall
Delete and reinstall Dilly. Your account and data live on the server, not the device, so reinstalling is safe.
Still crashing
Email support@hellodilly.com with device, iOS version, and what you were doing.