Chickens are notorious fraidy cats about something new. Try tossing something yummy in several days in a row. Once they get used to going inside it will be easier to coax them in. The other options is to catch them and lock them inside for a couple of days. Once they learn that the coop is home they should go back to it every night with no coaxing. It's just getting them in there.
The first night I transitioned mine into a new, larger coop you would have thought I was ripping their wings off. They were pitiful!! It took a couple of nights before they decided death wasn't imminent. Silly chickens.