Hi @Zoe Knecht ,
This is currently not possible in the desktop version of Microsoft Teams, there's an ongoing uservoice request for this feature in the Microsoft Teams uservoice page below:
https://microsoftteams.uservoice.com/forums/555103-public/suggestions/39353152-reply-to-specific-message-in-chat-on-desktop-app
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(If the reply was helpful please don't forget to upvote or accept as answer, thank you)
Best regards,
Leon