First be sure that it's not some kind of scam. Then do some research as to what is needed for a thriller.

Learning to write a genre one isn't familiar with is difficult under the best of conditions.

Have you read any thrillers? If you haven't, you should. See what you like and what you don't like about different ones. Start learning by reading.

You can find information about writing thrillers on line, research.

Then check again and again to make sure the ad isn't a scam.