Convert stringified double curly braces into variable

We have a make.com variable embedded within some HTML that we fetch from a HTTP GET call:

As you can see {{4.properties.firstname}} is found within an ‘HTML’ JSON node when fetched.

The issue we face is that this renders out literally as {{4.properties.firstname}} when we print this HTML node into an email, but I want this to be converted into a make.com variable?
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How do I make this happen?