Using the Tello only without the repeater, connect to the WiFi that ends in "Tello".
Using the repeater, connect to the WiFi that ends with "Tello plus" .
The repeater is the "plus" as it is an additional network that the Tello is connected to. If you use the repeater, the Tello connects to the repeater which "repeats" or strengthens the WiFi signal that the Tello emits and shows in the WiFi list as the Tello-plus network. Then when you connect your phone to the "plus" network, you are actually connecting to the repeater that is already connected to the Tello. If you connect to the network that just says Tello, then your phone is connected directly to the Tello and the connection is only as strong as the signal the Tello can emit on its own. The repeater acts more like an amplifier to slingshot the Tello's own signal further and stronger.