In the component editor make sure you have a new component, otherwise just create a new one by going to Component> add new to library. In some cases, such as this one, the component is already done for you. So lets just add it in.
Warning: make sure you don't have any finished component selected, as this step will replace it.
Go to Component > Get From Library
Skip the blue text if disc_sch (_discrete_sch.eli) is already there.
Click add and navigate to the library folder if you're not there yet (It's usually located in C:\program files\diptrace\lib). Select _discrete_sch.eli.
Select disc_sch on the left column and type switch10 in search and click search (don't press enter). only one result should show up, select it and press OK.

In the component properties box in the upper right corner input the following values: name = Switch, RefDes = S.

Now right click on the right sides and go to pin properties, change the value 20 to 3.

Save your work now.