Sure! Here’s the text with the correct prepositions filled in:

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Hey Henri,

Our computer club is meeting **in** September for the first time since the summer break. I’m looking forward **to** it. We’re meeting **on** Thursday, 2nd September **at** 6.30 p.m. We’re meeting **in** the same building, but it’s a different room. It’s **on** the second floor **at** the top of the stairs and **in** the right Room 2A. Let me know if you can’t make it.

Bye for now,

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Let me know if you need any more help!