using System;

using System.Text.RegularExpressions;

var rows = new[] {

    "Wed2,8-Jul-21 64 53,0 57",

    "Thu2, 9-Jul-21 73 60,0 48",

    "Fri, 30-Jul-21 86 70,0 36",

    "Sat,31-Jul-21 84 69,0 38",

    "Sun0, 1-Aug-21 89 73,0 33",

    "Mon0,2-Aug-21 98 80,0 24",

    "Tue0, 3-Aug-21 91 75,0 31",

    "Wed0,4-Aug-21 92 75,0 30"

};

​

​

var rg = new Regex(@"^(\w{3})\d?, ?(\d.*)");

​

foreach (var row in rows)

{

    var fixedRow = rg.Replace(row, "$1,$2");

    Console.WriteLine(fixedRow);

}