Registered for both groups, but want to appear for one

There is no Procedure of Cancellation or Intimating ICAI for Non appearence, & Nor is that Required. You can appear for G1 all 4 Papers & then not go for G2 exams. Remaining absent in One or more / all Papers of the Other group does not have any effect on the result ofthe Group in which you have appeared for all Papers ( G1 in Your case) If you score the required marks in all the Papers of that Group along with the Aggregate required for Passing the exam Then you will be declared as Passed that Group, Immaterial of whether you have appeared the Other group or No or Passed the Other Group or No. I hope your doubt is cleared