Hi and welcome to the forums @Chaya
The value shown on the printer screen is representative of the speed the printer is processing the file and printing. It is not an actual speed value, its purely a percentage.
If you want to adjust the speed of your prints you can do this within the slicer software by adjusting the speed parameters.
If you reduce the percentage on the printer then the print time will increase as you are asking the printer to not only print slower but also move slower during travels. Its always advisable to set your preferred speed in the slicer and only use the printer speed controls to slow the print down if you encounter issues.