PQ Matching data that doesn’t exactly match!

In that case, go through the following example based on your sample data set.

Modify it as necessary. But open a "BlankQuery" in power bi desktop, paste the following codes and run it to get some idea.

let

//your sample data set of "Seats" table
// Replace the following codes with your actual power query code that fetches the Seats table.

    Seats = #table(
        {"Train","Origin","Date","Time","Seats"},
        {
        {"A", "X",  #date(2018,4,1),#time(10,5,0), 186},
        {"B", "Y",  #date(2018,4,1),#time(11,40,0), 147},
        {"C", "Z",  #date(2018,4,1),#time(13,48,0), 167},
        {"A", "X",  #date(2018,4,1),#time(22,10,0), 191},
        {"B", "Y",  #date(2018,4,1),#time(23,55,0), 146},
        {"C", "Z",  #date(2018,4,1),#time(1,30,0), 170}
        }

    ),

//your sample data set of "Passengers" table.
// Replace the following codes with your actual power query code that fetches the Passengers table.

    Passengers = #table(
        {"Train","Origin","Date","Time","Passengers"},
        {
            {"A", "X",  #date(2018,4,1),#time(10,9,0), 149},
            {"B", "Y",  #date(2018,4,1),#time(11,51,0), 118},
            {"C", "Z",  #date(2018,4,1),#time(13,59,0), 134},
            {"A", "X",  #date(2018,4,1),#time(22,2,0), 153},
            {"B", "Y",  #date(2018,4,2),#time(0,2,0), 117},
            {"C", "Z",  #date(2018,4,1),#time(1,29,0), 136}
        }

    ),

// Add the date field and time field together to form a datetime column for operations

AddDateTimeColumnS = Table.AddColumn(Seats,"DateTimeColumn",each [Date] & [Time],type datetime),

// Reduce 2 hours from the DateTimeColumn added in the previous step as a new column "TimeWindowFrom"

AddTimeWindowFrom = Table.AddColumn(AddDateTimeColumnS,"TimeWindowFrom",each [DateTimeColumn] - #duration(0,2,0,0),type datetime),

// Add 2 hours from the DateTimeColumn added in the previous step as a new column "TimeWindowTo"

AddTimeWindowTo = Table.AddColumn(AddTimeWindowFrom,"TimeWindowTo",each [DateTimeColumn] + #duration(0,2,0,0),type datetime),

// Add the date field and time field together to form a datetime column for operations - To Passengers Table.

AddDateTimeColumnP = Table.AddColumn(Passengers,"DateTimeColumn",each [Date] & [Time],type datetime),

// Custom Function
// This function takes and Train Number, Origin, TimeWindowFrom, TimeWindowTo from Seats table and the entire Passengers table as input.
// It matches the details and returns the number of passengers as the list. 
// IF there are two or more trains matching all the criteria (a rare scenario), it returns the first match from the list

MatchTrain = (p as table,t as text,o as text,dtf as datetime,dtt as datetime) as number => 
    List.First(
        Table.Column(
            Table.SelectRows(p, each [Train]=t and [Origin]=o and dtf <= [DateTimeColumn] and dtt >=[DateTimeColumn]),
            "Passengers")
    ),

// Adds a column "Passengers" to the "Seats Table" after matching the details using the custom function "MatchTrain"

MatchedTable = Table.AddColumn(AddTimeWindowTo,
    "Passengers",
    each MatchTrain(AddDateTimeColumnP,[Train],[Origin],[TimeWindowFrom],[TimeWindowTo])
    ),

// Removes the unnecessary columns.

RemoveUnnecessaryColumns = Table.RemoveColumns(MatchedTable,{"DateTimeColumn","TimeWindowFrom","TimeWindowTo"}),

Output=RemoveUnnecessaryColumns

in
    Output

If you want to see the step by step operations, change the "Output=RemoveUnnecessaryColumns" line to each of the following and execute it. You will be able to see step by step output.

Output = Seats

Output = Passengers

Output = AddDateTimeColumnS

Output = AddTimeWindowFrom

Output = AddTimeWindowTo

Output = AddDateTimeColumnP

Output = MatchedTable

Output = RemoveUnnecessaryColumns