To Add the services:
Go to the "Setup".
Click on the "Services".
Click on "Add">> Add services.
4. Add the service, by filling up the required details.
5. Click on the "Save".
You may also rearrange the position of the service to be shown in the Quick sale by drop and drag method according to your preference, as shown below:
And the same order or position of the service will appear in the Quick sale while generating the Invoice.