Looking to catch a train to COLMAR upon arrival from CDG.
Taking the RER B train from CDG to Gare du Nord and walking from there is perhaps the simplest option.
You can also transfer from Gare du Nord to Gare de l'Est using Metro 5 in direction Place d'Italie, but you'll have to navigate some stairs up/down at either station. So it may be easier to just walk at street level with your bags. It's less than a ten minute walk between the two stations.