As per the information available, yes you can appear for the Improvement examination but for that you can only improve your last given examination & all the previous year marks will remain the same. If you wish to appear for the Improvement examination, then you need to fill the Improvement examination form by visiting the official website of SOL, DU & only then you can appear for the improvement examination.

For more information regarding the SOL you https://www.careers360.com/colleges/school-of-open-learning-university-of-delhi-delhi

I hope this helps. Have a great eve!