I have tested the behavior on Sitefintiy 7.2.5300 and Sitefinity 6.0.4200 and I was able to find the label in Labels&Messages section. For your convenience please review the video demonstration
I have created.
Please try to search for UserDisplayName and inform us of the results. Have in mind that in this Sitefinity version the search is case sensitive.
In case you are not able to find it you could add it manually by selection Create label button and adding the information below:
The label content
Dear <%\s*UserDisplayName\s*%>, we received a request for password change for username <%\s*UserName\s*%> at <%\s*SiteName\s*%>.<
href="<%\s*ConfirmationUrl\s*%>" target="_blank">Go to this page</
> to set your new password. The link will be active for one hour.<
The <%\s*SiteName\s*%> team
The body of the email sent to users for changing their passwords
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