To make something less harmful, serious, etc.
Make (something bad) less severe, serious, or painful.
Soil erosion was mitigated by the planting of trees. (Oxford)
It is unclear how to mitigate the effects of tourism on the island. (Cambridge)
soil erosion was mitigated
mitigate the effects of tourism on the island
Weaken
Lighten
Increase,
Extend
Mitigation
Mitigated