Save-PropertyMapping

# Connect to the source and destination sites
$srcSite = Connect-Site -Url "http://myfarm1/sites/mysourcesite"
$dstSite = Connect-Site -Url "http://myfarm1/sites/mydestinationsite"

# Get the source list from the source site
$srcList = Get-List -Name "mysrclist" -Site $srcSite

# Get the destination list from the destination site
$dstList = Get-List -Name "mydstlist" -Site $dstSite

# Retrieve existing property mappings between the source and destination lists
$mappingSettings = Get-PropertyMapping -SourceList $srcList -DestinationList $dstList

# Display the current property mappings
$mappingSettings

# Example output:
# PropertyMappings         :     Author        -> Author
#                            KEY Created       -> Created
#                                Editor        -> Editor
#                                Modified      -> Modified
#                                <NO SOURCE>   -> MultipleColumn
#                                MyCustomField -> MyCustomField
#                            KEY Title         -> Title
# ContentTypeMappings      : 
# UserAndGroupMappings     : 
# PermissionLevelMappings  : 
# SiteTemplateMappings     :
# SensitivityLabelMappings :

# Add a new property mapping for multiple source columns to a single destination column
$mappingSettings = Set-PropertyMapping -MappingSettings $mappingSettings -Source Col1,Col2,Col3 -Destination MultipleColumn

# Save the updated property mappings back to the source and destination lists
$mappingSettings = Save-PropertyMapping -MappingSettings $mappingSettings -SourceList $srcList -DestinationList $dstList

# Retrieve the updated property mappings to verify the changes
$mappingSettings = Get-PropertyMapping -SourceList $srcList -DestinationList $dstList

# Display the updated property mappings
$mappingSettings

# Example output:
# PropertyMappings         :     Author        -> Author
#                            KEY Created       -> Created
#                                Editor        -> Editor
#                                Modified      -> Modified
#                                Col1          -> MultipleColumn
#                                Col2          -> ───────┘
#                                Col3          -> ───────┘
#                                MyCustomField -> MyCustomField
#                            KEY Title         -> Title
# ContentTypeMappings      : 
# UserAndGroupMappings     : 
# PermissionLevelMappings  : 
# SiteTemplateMappings     :
# SensitivityLabelMappings :

Save-PropertyMapping
-MappingSettings <MappingSettings>
-SourceList <List>
-DestinationList <List>

Save-PropertyMapping
-MappingSettings <MappingSettings>
-FromFileSystem <SwitchParameter>
-DestinationList <List>