How can i solve this?
Including some screen shots of your events, and maybe describing what you have tried so far to fix it, will be a good start. We can’t read your mind 
Hello please explain what has to be solved in this post and all your future post.
The more detailed your request, the more likely you are to get a response.
A word or asking how to fix something is not a question.
the left arrow key slows down the enemy but won’t change the direction 180 degrees back when ive coded it too.
Like this
I think one of the two angles must be 0 and the other 180.
Or try to add some Object variable to the MrChomps like obj_var_direction = “right”
So you can check which is the current direction of each MrChomp and add force depending on that direction.
Condition:
MrChomp variable obj_var_direction = “right”
Action:
Add force at angle…
MrChomp variable obj_var_direction = “left”
Action:
Add force at angle…
Your last 4 lines are making life difficult for you. Get rid of the instant force actions with no conditions. They do nothing but force MrChomps to the left.
Then change the angle in the last event to 0 or -180, and make it a permanent force.