How do I enter health care coverage months from both 1095a and 1095c. I worked only part of the year.

You only need to enter information for any period of time where you had Obamacare or Marketplace insurance.  You will enter the information from Form 1095 A for this insurance.  You should enter the information only for the months you were covered by an Obamacare or Marketplace insurance policy.
 
For insurance offered through your employer, you will only enter that you were covered by insurance. No other information is necessary.