Edit the snippet in the Manager and click on the Properties tab.
BTW, SPForm should have asked you for the email address when you installed it. It should be set already.
Generally, it works as soon as it's installed in Revolution, with no configuration as long as you answer that question with your email address.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html