Ok I don't mind that u ask questions, but AT LEAST TRY to use the search to aswer your question
Region Override means that you can play games from another region (NTSC-J/NTSC/PAL whatever) on your own console. Standard these settings are locked so you can't play and import Japanese releases on your European console. Depending on what modchip you use, they have slightly different ways to change it... I thought Wiikey did it by onscreen settings, but others require to change a jumper on the printboard. Just google for the modchip you use to see how you have to change it.