OrderId   Name   JSON

{
    "Property1" :"",
    "Property2" :"",
    "metadata-department": "A",
    "metadata-group": "B"
}

declare @string varchar(1000) =
'{
    "Property1" :"",
    "Property2" :"",
    "metadata-department": "A",
    "metadata-group": "B"
}'


select SUBSTRING(@string, 0, CHARINDEX('"metadata-department"',@string)) + SUBSTRING(@string, CHARINDEX('"metadata-group"', @string), len(@string))

{
    "Property1" :"",
    "Property2" :"",
    "metadata-group": "B"
}

UPDATE TableX
SET JSON =
SUBSTRING(JSON, 0, CHARINDEX('"metadata-department"',JSON)) + SUBSTRING(JSON, CHARINDEX('"metadata-group"', JSON), len(JSON))

DECLARE @Text NVARCHAR(MAX) = '{
    "Property1" :"",
    "Property2" :"",
    "metadata-department": "A",
    "metadata-group": "B"
}';

PRINT dbo.RegExReplace(@Text, '"metadata-department": "[A-Za-z0-z]",rns+', '');

{
    "Property1" :"",
    "Property2" :"",
    "metadata-group": "B"
}