Network sepolia doesn't exist

**Describe the bug** A clear and concise description of what the bug is.

**To Reproduce** Steps to reproduce the behavior:

1. Go to 'ProjectNFT'
2. Build the project as instructed.
3. Error while deploying NFT.
4. See error after running below command
`npx hardhat --network sepolia run scripts/deploy.js `

**Expected behavior** Deploy the NFT on sepolia test net.

**Screenshots/ERROR**

> npx hardhat --network sepolia run scripts/deploy.js --show-stack-traces
Error HH100: Network sepolia doesn't exist
HardhatError: HH100: Network sepolia doesn't exist

**Desktop (please complete the following information):**

- OS [ MacOs Monterey (12.7)]
- Browser [Brave]
- Version [e.g. 14]