Both the regular eWAY and the newer eWAY RAPID payment gateways for your ONTRAPORT account use your same MYeWAY Account. ONTRAPORT and eWAY recommend using the new eWAY RAPID API method of connecting as described in this Knowledge Base article. But here are instructions if you prefer the old method.
You can find the information you need in your MYeWAY account.
For the ewayCustomerID use the CustomerID number found at the bottom of the screen when you log into your MYeWAY account, as shown in this image:
The ewayRefundPassword is actually the XML Refund Password that you set yourself in the eWay backend. Select the My Account tab, then eWAY Passwords > XML Refund Password:
In order to change the XML Refund Password you need to supply your MYeWAY account password first, then create the XML Refund Password. Be sure to put the XML Refund Password you create into the ewayRefundPassword field in ONTRAPORT, and not your MYeWAY account password!