How can we get the access_token using th refresh_token ?

I have these two code to get the access_token
1. Using fyers.generate_access_token()

 const fyers_access_token = await fyers.generate_access_token(reqBody)

2. Using API
   

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   const concatenatedString = process.env.FYERS_APP_ID + process.env.FYERS_SECRET_ID;
         console.log(concatenatedString);
         const hash = crypto.createHash('sha256').update(concatenatedString).digest('hex');
   
         const refreshToken = await fetch('https://api.fyers.in/api/v2/validate-refresh-token', {
           method: 'POST',
           headers: {
             'Content-Type': 'application/json'
           },
           body: JSON.stringify({
             grant_type: 'refresh_token',
             appIdHash: hash,
             refresh_token: decryptedCredentials.refresh_token,
             pin: ****
           })
         })

   In step 2, I want access_token without giving a PIN. How can I do this in Javascript?
   
   OR is there any other way to get the access_token token other than the one above?