Can you tell me how to get the measurement accuracy when measuring 0 to 1000°C with a type K thermocouple? I selected input type K2 (-270.0 to 1000.0).

Per the specifications, the accuracy of type K at 0°C or higher is ±0.1% ±1 digit. The measuring range in this case is that of the selected input type, -270.0 to 1000.0. You can calculate the accuracy as follows.
±0.1% of 1270°C = 1.27°C, plus 0.1°C of 1 digit = 1.37°C.