2 easy ways that I know of. I’m sure there are others. On a Windows PC:
If you need to do this for just a few words, go to Google Translate and set it for French to English. In the left box, it expects you to type the French word, so when you place your cursor there, the little French keyboard pops up, and the c with the cedilla will be there. Then you just copy/paste the text to where you need it. This is the fastest way I know of, for just a few words.
If you have to type in French extensively, then you need to load the French language pack that comes with Windows. Windows provides this pack for free, but typically it’s not loaded by default, you have to choose to do it. Go to Start/Control Panel, then click on Clock, Language and Region, follow the instructions to add your language pack. After you install this, you’ll have the option to switch between the English and the French keyboard at will.
And the good news is that when you go Microsoft Word, and you set your new blank page to French, you’ll be using that French keyboard.