DRDO CEPTAM

1) Firstly, explain your situation to them.
2) If you have photocopies of your 10th and 12th marks card then you could submit them. Also tell them you'll submit the duplicates of your marks cards at the earliest.
3) Your school and college will have a record of your 10th and 12th scores. So, approach your school and college from where you've graduated and ask them for a letter stating you've completed your education from that college/school.
4) Apply to your respective board for a duplicate marks card while also mentioning the reason for it. You might have to pay a fee for it which depends on the board. The sooner you apply for it the better.

If you are asking about the DRDO's MS recruitment. The eligibility criteria of DRDO's Multi tasking staff are given below.
1. Educational qualifications: 10th Class pass or equivalent from a recognised Board or Industrial Training Institute (ITI) pass. Candidates must have acquired the EQR as on crucial date of eligibility for the posts they are applying. Those awaiting results of the final examination as on crucial date of eligibility for the prescribed qualification are not eligible and hence should not apply.
2. Age : Candidate must be between 18 and 25 Years of age (Relaxable for SC/ST/OBC-NCL/ESM/ PWD/WIDOWS/ Divorced Women/ Women judicially separated from their husbands who are not remarried, Central government Civilian Employees, Disabled Defence Services Personnel, Persons Domiciled In Jammu & Kashmir State during the period from 01-01-1980 to 31-12-1989 as per extant government. Of India rules). As per the advertisement no. DRDO ENTRY TEST: 2019-20/MS for disability, you are falling under the Category-C with 18 number of reserved vacancies. Because you have completed your SSC in 1992 (before 27 years), So you are not meeting the prescribed age criteria of DRDO. So you are not eligible for these posts.