@waragandhi Welcome to the Workshop Community! Thanks for posting your question, no doubt others will join in the discussion.
Are you able to determine where the nest is, possibly a mound of sand/dirt with an entrance hole in the middle?
I would use this product Ant Killer Gel , you place a few drops at the entrance to the nest (or on the trail if you can't find the nest), the ants will take it back to the nest killing the queen and the colony.
This method will not effect your grass.
Hope this helps!
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Thanks for joining in the discussion on Workshop. Great to see you have already got some fantastic advice from Mitch. Please let us know how you go with following his suggestion.
Feel free to post on Workshop anytime you need a hand with anything around the house and garden. As you've already discovered, it's an extremely helpful community full of amazing people sharing helpful information, advice and project inspiration. We'd love to read more about your home improvement and gardening projects and plans.