Need help with merged columns and data types

You can first convert your text column to type time and then merge the 2 columns (first select the 2 columns) by using the Combine Date and Time functionality.

This is the generated code (with sample data in the Source step):

let
    Source = #table(type table[resolvedondt = date, resolvedontm = text],{{#date(2017,5,10),"3:39 PM"}}),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"resolvedontm", type time}}),
    #"Merged Date and Time" = Table.CombineColumns(#"Changed Type", {"resolvedondt", "resolvedontm"}, (columns) => List.First(columns) & List.Last(columns), "Merged")
in
    #"Merged Date and Time"

Here you can find Combine Date and Time: