I have an iMac. I turned off blue tooth. I have a bluetooth mouse, which I cannot use now. how do I proceed

My bluetooth mouse is not working. So I cannot navigate to System Preferences>Bluetooth.

The first several times I tried the Command <space bar> keys to select the Search window to type in Bluetooth File Exchange and then hit the Return key, nothing happened. After I got no responses on the community pages, I tried it again and it worked. I have no idea why it didn't work the first few times.