I'm a beginner and my photo was rejected.

Your rejected picture is highly underexposed, as can be seen on the histogram:

There are no whites, nearly no highlight in the picture.

There is also very little structure with your flamingos. It looks like you used a small sensor camera and the camera software eliminated this structure with its noise reduction. The same phenomena can be seen at the floor.

The plants in the foreground show artefacts and chromatic aberration.

I doubt that the corrected version will pass. But generally spoken, you are allowed to resubmit after corrections. I doubt, however, that you can correct this picture as much as needed to pass.

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

Both are poorly composed and underexposed with large out of focus elements in the foreground.

You should read and study ALL of the Help pages provided by Adobe Stock so that you understand the requirements before starting to upload images.

https://helpx.adobe.com/support/stock-contributor.html