Right click a blank area on the Toolbar, select Custom from the popup menu
that appears, select the Commands tab on the dialog box that appeared,
scroll down to the Macros entry in the Categories list, select the Custom
Button item in the Commands list and then click drag it onto the Toolbar.
After you release the mouse button, there will be a new icon on the Toolbar;
next, click the Modify Selection button that is on the dialog box and select
Assign Macro from the popup menu and complete the selection on the next
dialog box to appear. Then click the Modify Selection button again and
select Change Button Image if you want to use a different icon symbol for
your button. You can also play with some of the other items on the popup
menu from the Modify Selection button.