When you want to express "thank" or "sorry" for something, you have to notify that Korean language is not changeable word-to-word.
thank for the flower.
= 꽃을 선물해줘서 고마워.
In this case of "for the flower", there is no verb or verb variation, so you have to guess the proper and suitable verb, as above example of "present"
But don't worry too serious.
basically "thank you for sth", or "sorry for sth", is "~해서 고마워","~해서 미안해"
p.s) Thank you in advance = 미리 고맙다는 말을 남깁니다. = 미리 고마워 (awkward, but understandable)
(actually in korean language, there is no exactly correspondant expression)