How to Change Default validation massage "Please enter a value with a valid mimetype."

Question

I just started using jquery and I'm using this code for validation

if (flag == "national_id" || flag == "selfie_with_id") {        
    $('input[name="file_upload"]').attr("accept", "image/jpeg,image/png" )
    $(".file-upload-type").text("* .jpg, .png, Maks. 2Mb");   
} else {
    $('input[name="file_upload"]').attr(
        "accept",
        "image/jpeg,image/png,application/pdf"
    )
    $(".file-upload-type")
}
return false;

how do I adding validation massage?