To change Wi-Fi settings, access the hidden admin sidebar:
Make sure the device is on and unlocked.
Locate the power/lock button (usually top-right or right side).
Quickly repeat the following sequence until a purple arrow appears in the top-right corner:
Tap the top-right corner of the screen
Press the power/lock button
Tap the top-right corner of the screen
Press the power/lock button
Repeat...
Tap the purple arrow to open the settings sidebar.
Update Wi-Fi as needed. When finished, lock the device. The arrow will disappear shortly.