Scan the QR code on your Mini's screen, or enter the six-digit code shown under it. Only that Mini is changed by what you do here.
New Mini with no Wi-Fi yet? Its screen shows a Wi-Fi QR code: scan it, join the Mini-xxxx hotspot and choose your network on the page that opens. The Mini then shows its six-digit code and this address.
Away from the school Wi-Fi? Every Mini keeps its own hotspot Mini-xxxx switched on: join it and open http://192.168.5.19/settings (any address works there) to change its Wi-Fi, name, language, character and behaviour with the code. The Mini sends the changes to the school as soon as it is online.
Lost the code? Ask the school office: the server lists every robot's code. Restarting a Mini that has not been claimed yet shows the code again.