Welcome to Week Tally help and support.
Go to Settings and tap Reset the app. Bear in mind this is non-reversible and will delete absolutely all of the data you have logged so far. You may wish to instead delete Things (Settings > Things tracked > tap the 3-dots icon) or toggle some Things off.
In Settings, tap Daily Notification Time and follow the instructions.
Please open a new Issue here: https://github.com/Yorkshireman/week-tally/issues/new