pencil (something or someone) in
idiom

- to put (someone or something that may be changed later) on a schedule, list, etc.

"Would you like me to pencil you in for Thursday morning at 11.00?"

sometimes used figuratively:

"He was penciled in as the director's replacement."

Merriam-Webster

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WORD ORIGIN

Pencil in means to tentatively set up an appointment, so as to reserve time, but to allow the appointment to be readily cancelled and replaced with another.

The notion is that something written in pencil is more easily changed than something written in ink. This phrase originated in the "old" days before the advent of electronic calendars in computers, tablets, and mobile phones.

Pencil in is commonly used in the early stages of organising a meeting with multiple people, before it is known whether all attendees will be free at the suggested time. It can also be used when talking about scheduling an event, such as a product launch.

The phrase is also common in sports to note when a player is scheduled to start a game (Joe Miller has been pencilled in for the game against Manchester this evening). This originated from the custom in American baseball in which the manager fills out a card with the names of all the starting players and hands it to the umpire before the start of the game.

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Practice OWAD in a conversation. Say something like:

"I've got you PENCILLED IN for the next staff meeting, OK?"