Remove-PropertyMapping

# Initialize the mapping settings with the first property mapping
# Mapping "MyColumn1" to "MyColumn1" and designating it as a key column
$mappingSettings = Set-PropertyMapping -Source "MyColumn1" -Destination "MyColumn1" -Key

# Add a second property mapping to the existing mapping settings
# Mapping "MyColumn2" to "MyColumn2"
$mappingSettings = Set-PropertyMapping -MappingSettings $mappingSettings -Source "MyColumn2" -Destination "MyColumn2"

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

# Remove the previously added mapping for the "MultipleColumn" destination
$mappingSettings = Remove-PropertyMapping -MappingSettings $mappingSettings -Destination MultipleColumn

# Output the final state of the mapping settings object
$mappingSettings

# Example output:
# PropertyMappings         : KEY MyColumn1 -> MyColumn1
#                            MyColumn2    -> MyColumn2
# ContentTypeMappings      : 
# UserAndGroupMappings     : 
# PermissionLevelMappings  : 
# SiteTemplateMappings     :
# SensitivityLabelMappings :

Remove-PropertyMapping
-MappingSettings <MappingSettings>
-Destination <String>