How to get a technical resignation for Government job

Already they have given you a NOC for attending the interview. But now they are not relieving you. There is no much difference between resignation and technical resignation. If you apply for a new post through proper channel or informed them before joining about the post you have applied already before joining your resignation will be treated as Technical resignation only, even though you have not used the word Technical. So you have to submit your resignation once you get the selection.
When you joined in this post you might have signed an agreement with the organisation in which they might have mentioned about the rules and regulations and terms and conditions. You have followed those issues while residing in the post. They will relieve you and if they don't treat your resignation as Technical Resignation. The benefit of past service may not be given to you if they say your resignation is not technical and they may relieve without any problem. You can refer to the office memorandum No; No. 28020/2/2018-Estt. (C) dated 27th August 2018 for further details.

While joining DRDO, you might not furnished the details of the nature of examination in the personnel form issued by the personnel department. Though it was a minor lapse but attracts disciplinary action if your organisation wants due to omission of the facts.
However, the result of the said examination was communicated from your end and for the same you got NOC for the interview.
Had there not been any suppression of the fact relating to your previous appearance in the examination, your application could have moved through the proper channel to the organisation for which you are the eligible candidate. Resorting to such a rout is known as the basis of technical resignation. The application could have reached to the organisation through your parental department.
In your case, it would not be applicable and once you are selected for the post of the next organisation, you have to tender your resignation known as ordinary resignation depriving you benifits which otherwise you could have got in case of your protection of pay, seniority, transfer of leave and transfer of PF and Gratuity already enjoyed in the present organisation.
Though they will accept your ordinary resignation, you will be deprived of the facilities already indicated above.