Ok so you need to put a picture in his head. Of you. Wanting him. Of you and him.
Not knowing either of you or the context is a shot in the dark but you have various basic options:
Go sensual
Describe/suggest some physical experiences that will lead his imagination.
Eg:
[Disclaimer: these are pure cheese obvious examples just to give OP the general idea - need to be tailored to suit!]
'Omg just had the nicest bath ... got this amazing bath oil and my skin feels so smooth now ... pity am all alone ☺️'
''Lying in my bed but don't feel like sleeping for some reason ... obviously haven't had enough exercise today 😉'
[i did say these were shamefully Tesco Value comments!]
'So annoyed - got some super silky (and bloody expensive!) stockings online and they come too far up my thighs 😬 (TBVH I like just a little bit of naked flesh at the top - I know 😂 V naughty of me. I like standing in the queue in Costa and knowing I have literally the sexiest stockings hidden under my skirt. Clearly am in need of help!')'
Ok have to go now but will continue later with some more horrific cheese that does the trick even if embarrassing 😂
Remember: sex is just sex. It's pretty simple. Appeal to his base instincts. But why I say knowing him is important - more because he will have a view of you, and you don't want to mess with that by being weirdly OTT. You just need to work out the best way to show him the green flag.
I never cease to be amazed by how guys will actually tell you within 10 seconds how much they want you, if you just pay attention to the signals.