1.Go to the official website of DU and fill the application form.
2.Opt for the ECA category and the corresponding activity through which you want to qualify.(for you, Dance)
3.Upload your ECA certificate as evidence of your participation in the respective activity.
4.The certificate through which you are applying must not be more than three years old.
5.Your candidature for the ECA category will be considered only if you have won or participated in the respective ECA activity at International, National, State, Zonal or School level.

There is a selection process for the same-
1.According to the rules of DU, you will be eligible for ECA seats if you have a valid certificate for the respective extracurricular activity.
2.You will also have to qualify the Trials conducted by DU.
3.DU gives 25% weightage to certificates, whereas, 75% weightage is given to ECA Trials.
4.Trials will be conducted at the Preliminary and Final level.
5.All candidates are allowed to appear for preliminary trials only once.
6.Those who clear the preliminary trials are then called for final trials.
7.It is important to secure at least 50% marks i.e. (38/75) in the final trials in order to qualify through ECA quota admissions.

Merit list will be prepared by the authorities on the basis of final trials and their percentage in class 12. Admissions will be done on the basis of this list.
The details regarding the ECA Activities and schedule of ECA Trials is provided on the official website of DU. The University and colleges conducting trials also release notices regarding the same both online and offline.

I hope the detailed information is worth and helpful! :)

All the very best!