What does it mean?
I'm not sure what the first game to do this was, but a "tell" is a private message sent to another player. I think it originates way back from text-based MUDs where to message someone you'd type something like
These days many multiplayer games call those messages "whispers" instead, but often
So, "please send tell" basically means "contact me privately to respond".
Another meaning is "Pacific Standard Time," a time zone eight hours west of Greenwich, used by places like Los Angeles (movies, games,) San Francisco (start-ups, games) and Seattle (Microsoft, games.)
If you're talking about scheduling of events, then this is a much more likely meaning of the acronym.