Basic re-tuning normally only takes a few minutes:
Switch on your Freeview TV or box and press 'menu' on the remote control
Select the 'set up' or 'installation' option then ‘first time installation’ option (sometimes called 'factory reset', 'full retune’ or 'default settings').
Press ‘OK’ if your equipment asks if you want to delete all your channels Don't worry this is normal.
If you are prompted for a code, try 0000 or 1234. Channels will be automatically installed. Your equipment may shut down and restart.