Marli loves Starly, so she asks you to show her the pokédex entry for Starly.

The Request

Talk to Marli in front of the General Store in Jubilife Village to start her request.

Complete Starly's Pokédex Entry

Starly can be found in the Obsidian Fieldlands, in the following areas: Aspiration Hill, Horseshoe Plains, Windswept Run, Tidewater Dam. Catch or battle Starly to add it to your Pokédex. Complete research tasks until the entry's Research Level reaches 10. Then talk to Marli again to show her the completed Pokédex entry.

Show Marli a Starly

Now you will need to have at least one Starly. When you do, talk to Marli and show her one. (She won't take the Starly; she will just look at it.)

Reward

After you show Marli a Starly, you get 10 Poké Balls.