I flunked my first year B.Com. Can I continue my 1st year and 2nd year simultaneously?

It depends on the rules and regulations of your university or college. Generally, if you have failed in your first year, you will need to clear all the subjects before proceeding to the second year. However, some universities or colleges may have provisions for reappearing in the failed subjects in

You cannot do 1st-year and 2nd-year simultaneously, yes, if you are in the second year then you can write all the first year subjects now or in November with second-year subjects.