Google keeps adding useful features to Gemini, including this latest, from 9to5Google:

Google is launching “a more precise way for you to tune Gemini’s responses” on the web app. 

When selecting (by highlighting) a part of Gemini’s response to your prompt, a pencil/sparkle icon appears to “Modify selected text.” This opens a box with Regenerate, Shorter, Longer, and Remove options, as well as an open text field. 

As the best prompts are iterative – getting closer and closer to the desired response – this is a great way to work.

Read about that here.