How to modify a variable in RITM using REST API?

[Apex Predator]

I have a catalog item with a few variables. I am able to create RITM's for this. But I want to modify an RITM at a later time i.e I want to update one of the variable's value of the RITM using REST API. How can I achieve this? Is there an out of the box API to do this?
Thank you

[Ankur Bawiskar]

@Apex Predator 

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Ankur