CMS Global Tags for Conditions Data:

• https://twiki.cern.ch/twiki/bin/view/CMSPublic/SWGuideFrontierConditions

How to change it?

process.load("Configuration.StandardSequences.FrontierConditions_GlobalTag_cff")
from Configuration.AlCa.GlobalTag import GlobalTag
process.GlobalTag = GlobalTag(process.GlobalTag, 'auto:run2_mc')