Assuming you can't boot into the sysmenu and didn't region-change a Korean (NTSC-K->NTSC-U) console
Load DOP-Mii and choose IOS 249/250 at the top of the first screen
Scroll to the right until you highlight IOS70
Press (+) to install and confirm Trucha/fakesign, ES_Identify, and NAND Permissions
Select Download from NUS (assuming you're online, if not follow the instructions on the op for offline installs)
Confirm if asked until the download/install completes
After that's finished get back to the DOP-Mii Main Screen
Scroll down to System Menu and press A
Select System Menu 4.2
Select Your Region [VERY important]
Once again press (+) to install and confirm until it completes
*It shouldn't ask you to reinstall your system IOS (you just did in the first step above), but if it does you can say yes again and go through the above procedure.
**If your console was originally NTSC-K and converted at a later time to NTSC-U, don't follow these instructions.
Assuming the installer did not give you special instructions or any warnings or errors, your system menu should load now. Before leaving DOP-Mii you can confirm the success of your installation by running a Syscheck through the main menu. Once you've confirmed a successful install, exit and reboot your Wii.