I can’t find Arduino MCU
In the “Parts” window, click on the “CORE” bin, then scroll down to the Microcontroller section. The first entry there should be an Arduino UNO. Drag that into your sketch, then in the “Inspector” window, select one of the variations from the “type” drop down. There are more than 20 to select from.
senseBox MCU is the boards name???
That can be used with the Arduino IDE, but it is not really an Arduino board. To be able to add that to Fritzing (as a part), detailed specifications will be needed. A data-sheet with physical dimensions and pin position information, plus electrical specification, on what each of the pins are.
A google search for “fritzing part sense box mcu” turns up a not very good part at
which may do what you want.