Hi Mitra,
Your subscription is not eligible for Bing Grounding Search SKU G1 access.
You have to upgrade your subscription to Pay-As-You-Go, as Grounding with Bing Search costs $35 per 1K transactions.
After you upgrade your subscription, here is the supported documentation for using Grounding with Bing Search:
https://learn.microsoft.com/en-us/azure/ai-foundry/agents/how-to/tools/bing-grounding
Feel free to accept this as an answer.
Thankyou for reaching out to the Microsoft QNA Portal.