I got rejected because of quality issues

Previews are too tiny to critique. 

Check your full sized images at 100-300% magnification for proper focus, exposure and color balance.

Make adjustments if needed in Photoshop or Lightroom. 

Adobe Stock customers expect the highest visual and technical quality for use in commercial projects.

• https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
• https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html
• https://helpx.adobe.com/stock/contributor/user-guide.html/stock/contributor/help/photography-illustrations.ug.html
• https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html

You need to post one or two of your assets here, in the same quality as submitted. we can have a look into them. 

Or you check your assets yourself at 100%. If they are unsharp or have artefacts, you should see that. 

If you are new to stock, you should consider these resources: https://helpx.adobe.com/stock/contributor/tutorials.html
Please read the contributor user manual for more information on Adobe stock contributions: https://helpx.adobe.com/stock/contributor/user-guide.html
See here for rejection reasons: https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html
and especially quality and technical issues: https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

Sorry Shuvo! It's impossible to make an assessment with what you are sharing