Try restarting (turning the phone off and back on) and see if it will let you in then. Otherwise the only way I know of either involves clearing that apps data (which would erase anything in it) or uninstalling and reinstalling the app, which would again effect your data. You need to contact the apps creators to see if they have a fix if turning the phone off and back on doesn't allow you in.
In the future I would really suggest backing up things you want to keep off the device. To a google or cloud account, or to a computer. It is much safer that way.