Its very good that you are preparing for a reputed exam very early .

So to give the ias exam the minimum eligibility is that you must bachelor degree holder

In order to complete your degree you must concerned about the course so which course you will choose and that course will directly affect your IAS preparation

as you know the examination pattern prelims then Mains and then personality interview

prelims contents of GS and CSAT

and the main exam consist of 7 exam each of 250 marks in which four are GS papers one is essay writing two exam are of one optional subject total of 500 marks

and the personality interview is of 275 marks

so here is a total of 2025 marks in which about 700-800 you will need to score rank.

So now 500 marks of optional subject plays a major role in total of 2025 marks

Now in order to complete your degree you must choose that particular optional subject in which you have interest , you never become bore while reading it n number of time.

So the question arise that what should i do either Bsc BA BE BTech Bca Bba etc etc. These are the bachelor degree that must be complete to be eligible .

You have many option after completing your 12th.

I am going to tell you a five step procedure by which you will know that which course you should choose and in which field ( subjects) you are capable of .

Step 1 : Read all ncert books of 11&12 class of each and every subject.

Step 2 : now choose minimum 3–4 subjects in which you are interested or you are capable to understand it in deep.

Step 3 : find out the previous papers of those 3–4 subjects . .

Step 4 : match the syllabus with the paper.

Step 5: try answering the questions of topics that you have gone through.

Now completing all these steps you will find out your optional subjects. So on the basis of optional subject you will pursue your degree . It is not important that you are from pcm background you must do B.Tech or BSc. You can simply do BA with your optional like history geography etc. If you want to do engineering than see the syllabus of each stream electrical mechanical and civil as well . See whatever branch suits you.

All i want to say that pursue your degree of that course in which you can master yourself , upsc needs masters of their subjects .

Do not deviate by someones guidance . Go through youtube, search ias preparation , about ias , syllabus , exam pattern etc you will find a bulk of knowledge from there .

Wish you luck .