text to date format

Split first your column.

Then Merge them with space then change data type to Date Time.

Here's a guide

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjDUD04t0DcyMLS0MjC1MgGSlkqxsQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Column4.2 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column4.2", type text}}),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Changed Type", "Column4.2", Splitter.SplitTextByEachDelimiter({":"}, QuoteStyle.Csv, false), {"Column4.2.1", "Column4.2.2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Column4.2.1", type date}, {"Column4.2.2", type time}}),
    #"Merged Columns" = Table.CombineColumns(Table.TransformColumnTypes(#"Changed Type1", {{"Column4.2.1", type text}, {"Column4.2.2", type text}}, "en-GB"),{"Column4.2.1", "Column4.2.2"},Combiner.CombineTextByDelimiter(" ", QuoteStyle.None),"Merged"),
    #"Changed Type2" = Table.TransformColumnTypes(#"Merged Columns",{{"Merged", type datetime}})
in
    #"Changed Type2"