@Galvile,

If the device has become disconnected, you can first try simply rebooting the camera - as this will force the camera to look for the wifi network.

Otherwise, if the device cannot reconnect to your network, you would need to reset the camera's network settings and re-setup the camera from the Tapo App. 

You can reset the camera by holding the reset button for up to 15 seconds (at 15 seconds, it will become a factory reset). 

A soft reset such as this will only erase the camera's network settings and will keep everything else. 

Using the Tapo App, you can then configure the wireless settings for the camera using the regular setup process and confirming your previouse settings.