How to?

Sooo...this is a stupid question but idk how to wake up a guy by giving him a bj. I’m 23 and my boyfriend has always wanted me to wake him up that way but I just never have. How do I do it? Like just play with it first? And then start sucking after it gets hard? Lol it just sounds weird to me. Will it still get hard even though he’s asleep? Sorry this is so embarrassing to ask 🤣 I mean I know how to give a regular bj but just the fact that he’s asleep during it throws me off 🤣