Hanging basket camomile

Hi there, this is my first ever post! I'm basically a complete begin when it comes to gardening, after having always lived in flats. Please bear with me if this seems like a silly question! I have camomile growing in my herbaceous hanging basket and the flowers are starting to die off now and it is becoming a bit limp. I know I need to be trimming it back but I'm not sure how much. 

Please can someone give me some instructions on how to prune it back. 

Also the leaves are going a lighter colour. I'm worried that I've over watered it!! 

If this is  not the correct place for asking this im sorry!! 

Thank you in advance x