It seems† this refers to https://intelilight.eu/ (as referred to from https://www.flashnet.ro/project/intelilight/). And it seems you’d not only need to send sensor data to them, but they also need your gateway(s) to transmit downlinks to control the (street)lights?
If yes: you can’t.
If no downlinks are needed, or if you can handle those yourself rather than them having to control your gateway(s), then you need to set up an application outside of TTN, which gets its data using the TTN MQTT Data API or one of the integrations, and which then forwards the data to that third party.
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† Geheimtipp: don’t expect people to investigate for you if you need help. Also, this is getting quite off-topic for your initial question.