duplicate marksheet got rejected. Please help

What is the reason given for rejection?

If it is disputable then you can challenge the decision 

You were required to upload the original document or attach an affidavit to express that since you had lost your original document, you obtained the duplicate hence the same has been uploaded.

However if there is no provision for uploading the affidavit or the duplicate document, then you may have to write to the recruitment authorities in this regard explaning the circumstances under which you relied upon the duplicate documents. 

If it is an applicaiton for government job then you can resort to file a writ petition seeking court intervention in this for a direction to the recruiting authorities to accept the duplicate document if found to be genuine.

You should follow the procedures of law for obtaining the duplicate copy of the documents. 

If it is a certified copy then the recruitment authority would have considered if it was accompanied by an affidavit. 

You can introspect what and where it went wrong so that you can rectify the error for future issues 

If you had followed the due process of law to obtain duplicate copies then the documents so procured are genuine. 

In that case you can proceed legally by filing a writ petition before high court seeking intervention 

repeared.