firstly go to your kindle settings and check if kindle airplane mode is on or off if it is off then try to restart your kindle device by holding the power button for 30 seconds then release it as the light of the kindle goes off wait for a while then again restart the device. if still, the kindle device wont connect to wifi then try to connect other smart devices to the wifi network and check whether the same issue arises in their case or not if not then you need to update your kindle software