I think you might be slightly confusing things. Following Nicholas II's abdication from the throne and the creation of the Russian provisional government after the February revolution in 1917, Lenin was given passage through Germany by the Imperial government in Berlin to return to his home country. The Germans knew that Lenin and his Bolsheviks would cause problems (read: raise hell) in Russia, potentially aiding the Germans indirectly and possibly even ending the war in the East (which is exactly what happened).

Afterward, during the Russian Civil War, many German veterans (commanders and frontline soldiers alike) offered their services to the pro-White forces, and while their reasons varied greatly, many felt the establishment of a communist state nearby would further destabilize the already weary legitimacy of the new Weimar Republic, which was then dominated by the SPD (Social Democratic Party). Many other ethnic Germans that fought against the Bolsheviks were also Baltic Germans, who feared reprisals by the Bolsheviks once they established control over Russia.

Initially, German troops in the east fought with the Bolsheviks periodically, defending the gains made by the German Empire at Brest-Litovsk. Once these gains were made forfeit, however, by the Armistice and de facto surrender of the Reich, the Germans were allowed to maintain their 8th Army in the former Ober Ost, to help stem the westward expansion of the Bolsheviks. They operated along with paramilitary Freikorps, such as the Iron Division, but once the Treaty of Versailles was signed, these forces were to be disbanded. A British Army mission led by General Hubert Gough was dispatched to the Baltic states, tasked with the mission of organizing resistance against the Bolsheviks, and disarming the German forces there (especially the Iron Division).