Passing GUID of a related entity record in a workflow email

Hello guys,

Here is my problem: 

I have two entities :  Account and Account Approval.

 In the account entity, there is a button which when clicked will trigger an on demand workflow. This on demand workflow has a couple of steps. It first checks a condition and if it is met will create a new record of account approval which is linked to account. Next step is, it will send a new email to certain users. 

The issue is , in the email there is a hyperlink to a third party site. This URL needs the GUID of the account approval record created corresponding to the account record. How do I get the GUID of the account approval record and pass it in the URL ??