Need your assistance to create a F5 redirection rule for /user/login.seam -> /login

give a try

option 1

when HTTP_REQUEST{
if { [string tolower [HTTP::uri] ] ends_with "/user/login.seam" } {
  HTTP::uri [string map {"/user/login.seam" "/login"} [HTTP::uri]]
  HTTP::redirect "https://[HTTP::host][HTTP::uri]"
}
}

option 2

when HTTP_REQUEST {
    if { ( [string tolower [HTTP::uri]] ends_with "/user/login.seam" } {
        set uri [HTTP::uri [string map {"/user/login.seam" "" "/login" ""} [HTTP::uri]]]
        HTTP::redirect "https://[HTTP::host]$uri"
    }
}

I would use

HTTP::path

rather than

HTTP::uri

, because the URI could include a query string and hence the comparison would fail.

when HTTP_REQUEST {
  if { [HTTP::path] ends_with "/user/login.seam" } {
      HTTP::path [string map {"/user/login.seam" "/login"} [HTTP::path] ]
  }
}

As Michael noted, you must be careful with upper/lower case comparisons. For completeness' sake, this ought to work in all cases (no pun intended):

when HTTP_REQUEST {
  if { [string tolower [HTTP::path]] ends_with "/user/login.seam" } {
      HTTP::path [string map -nocase {"/user/login.seam" "/login"} [HTTP::path] ]
  }
}