If we made a large moon near Mars, the tidal forces would encourage the tectonic system to rev up again, and start up the inner dynamo effect. There would be volcanoes, producing a new atmosphere, which would capture more of the sun's heat and promote warm humid conditions for life.
To make the moon, it would be necessary to merge Phobos and Deimos and to figure out a domino effect among large bodies of the solar system which would send them all into the same orbit of Mars somewhere where they would join up.
Would we be able to make Mars have oceans again?
What technology plans could we develop to make a new moon possible?