The Hammers were thumped 3-0 at the City Ground yesterday.
"It’s not good enough and obviously, when you go down to ten men, it makes it harder again,” Bowen told Premier League Productions.
“Going in 1-0 down at the break with eleven men, we knew we would still have been in the game, but with ten, obviously it was even more difficult. But those are the circumstances that we were in, and it was important at 1-0, it's only one goal.
"They've obviously got a man more, but it's about being clever and not conceding, but we didn't manage to do that and in the end we conceded two and it could have been more so it’s frustrating, for sure.
“I think we've got to accept the defeat and understand the feeling and how we're all feeling now, we have to go forward and not want this feeling again.
“We've been on the receiving end of a lot of defeats by a lot of goals, so we need to look at ourselves as players. I think that's a given, but I think we've got to accept this feeling, accept it today, move on tomorrow and in the last game before the international break we have to put it right and that's it.”