Download <<
audacity.sourceforge.net/|nya>>
Set the highlighted thing <<
i.imgur.com/XISxRNb.png|nya>> to whatever your speaker output is called
Start playing the thing dunkel linked
Press record
Go get a snack, eat it, return to keyboard
Press stop
File > export > save
Also you can just make your own in Audacity but that is a little more involved and you have to know soundmath to get the frequency you want. To do that just go Generate > Tone, set the values, then repeat until you've got the frequency you want.