To get to this location, you'll have to use the geysers on the islands to push yourself up and then paraglide across the lake. Eventually, you should see a cannon, which you can load with a bomb and shoot towards the vault, which will free Yunobo. Once free, talk to him and then ...
select "Downloads," and in the "Limit Bandwidth" field, set the value to 100,000 (the Reddit user says the number doesn't matter as long as it's over 1,000). Then, hold the power button and switch to the desktop. Click on the Wi-Fi symbol in the bottom right corner. In the ...