[Dan.]

Below your includes:

pawn Код:

new ClassSelected[playerid];

under OnPlayerConnect callback:

pawn Код:

ClassSelected[playerid] = 0;

The command:

pawn Код:

CMD:resetclass(playerid, params[])
{
    ClassSelected[playerid] = 0;
    SendClientMessage(playerid, C_LBLUE, "Class selection when you spawn!");
    return 1;
}

under OnPlayerSpawn callback:

pawn Код:

if(ClassSelected[playerid] == 0)
{
    ClassSelected[playerid] = 1;
    ShowPlayerDialog(playerid, 999, DIALOG_STYLE_LIST, "{6EF83C}Choose A Class:", "Assault Class  (Need No Rank)  \nSniper Class  (Need Rank 2) \nMedic Class  (Need Rank 3)  \nEngineer Class  (Need Rank 4) \nMercenary Class  (Need Rank 5 )  \nJet-Trooper Class  (Need Rank 7)  \nPilot Class  (Need Rank 8) ", "Choose","");;
}

E:// Sorry, I misunderstood. If you want the player to respawn at his base after that, then just use SpawnPlayer(playerid); Although I wouldn't use it, because it would get abused (teleporting away when low HP).