Since the Rockies signed Daniel Murphy to play first base, he will displace Ian Desmond from first base (to the happiness of a lot of Rockies fans). However, with his contract, Desmond will still almost definitely be playing everyday, much like Rockies manager Bud Black deployed Desmond in 160 games (149 starts) despite a subpar season both offensively and defensively.
With having past experience in playing both center and left field, Desmond will move to the outfield.
But there will likely be another change in the outfield involving Charlie Blackmon. Blackmon has patrolled center field for the Rockies on a full-time basis since 2015 but in 2018, he saw his defensive metrics plummet.