[Alex_Valde]

You need to watch your coding style. It's a little strange.

pawn Code:

dcmd_setplayerhealth(playerid, params[])
{
    new targetid, amount;
    if(!sscanf(params, "ud", targetid, amount))
    {
        if(IsPlayerConnected(targetid))
        {
            if(amount > 1 && amount < 101)
            {
                new playername[MAX_PLAYER_NAME], targetname[MAX_PLAYER_NAME], string[128];
                GetPlayerName(playerid, playername, sizeof(playername));
                GetPlayerName(targetid, targetname, sizeof(targetname));

                format(string, sizeof(string), "%s(%d) set %s(%d)'s health to %d", targetname, targetid, playername, playerid, amount);
                SendClientMessageToAll(0x50FF05FF, string);

                SetPlayerHealth(playerid, amount);
            }
            else return SendClientMessage(playerid, 0xFFFFFFFF,"Error: Please use |Max|: 100, |Min|: 1");
        }
        else return SendClientMessage(playerid, 0xFF0000AA, "Player not found");
    }
    else return SendClientMessage(playerid, 0xFF0000AA, "Usage: \"/setplayerhealth <playerid> <amount>\"");
    return 1;
}

EDIT: JaTochNietDan already helped you.