A presentation swap fails when the ask is a mood. "Hey, I might need to switch my day, no worries if not" gives the other person nothing to accept. They will say "maybe" and both of you will stay on the original slots.
Name the trade. Your date for theirs. One fact that makes the trade necessary. A yes they can send in a line.
Two slots, one sentence
"I am on Tuesday the 4th, you are on Thursday the 6th. Will you swap so I present Thursday and you present Tuesday?" That is the whole decision. Ask for it with the list closed: swap, or keep the posted order.
Give one reason a cold reader can hold: a documented exam that day, a travel date already booked, a lab you cannot leave. Do not send the week of conflicts. Do not send the chat where you talked yourself into asking.
If the instructor has to approve any swap, say that in the brief and make the classmate's reply the first yes, not the last. Two owners in one message is how you get neither.
Make no cheap to say
Tell them that no is fine and needs no explanation. A written no should cost less than a delay. "If you want to keep Thursday, say so — I will present Tuesday." That sentence is the entire courtesy.
Give a deadline that is real. The instructor locks the order on Friday. After that you will not ask again. A soft "whenever" is how the swap dies in the thread and you still panic on Monday.
Do not offer three alternative weeks. One trade. If they counter with a third date, that is a different decision and a different message.
Send a briefing, not a thread
You draft. You read. You confirm the send. A classmate should not receive a message that sounds like a different person because the model warmed up the tone.
They do not need an account. Email and a link are enough. If they already have RelayLink, you need an accepted contact. Invite once if you will keep writing this way.
No attachments. The slide deck stays in the course folder. The briefing is the swap.
Nicknames stay private unless you share them. Use the name on the roster.
If they block you, the block is silent. Present on your day.
When the trade fits in one sentence, connect your assistant and ask for the yes before the order locks.