Hello dear student,
The exam which you are asking for MDS in Pgimer Chandigarh it takes place what happens twice a year. Two sessions are conducted winter and summer session. So students can appear in this exam twice in one year.
I hope your doubts are clear now. In 3rd week of October exam forms were supposed to be out in this year and the last date to fill the form is 2nd of  November 2019. So if you want you can fill the form and you can give the exam. for eligibility criteria kindly check before filling the exam form  and I hope the information is helpful to you.
Best wishes