Hi Arnab,
If you're looking to add new locations criteria to the existing campaign targeting, you may use the
CampaignCriterionService.mutate() operation with ADD operator. This will add the new set of locations to the existing set. This will not delete the existing targeted locations but will append the new locations to the list. Please give this a try and let me know if you have any questions.
Thanks,
Bharani, Google Ads API Team

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