Assuming you’ve already talked to the person: make that player wait to contribute. After you describe an area/object/whatever you go around the table rather than addressing the group; look at each player and use their name (or char name) asking what they’d like to do. Put the talker last about half the time and in the middle the other half. This makes it clear you want everyone to have time to speak.

If the problem doesn’t get better, and the other players are unhappy, ask the talker to leave.

As a player, when I see another player constantly getting talked over, and it’s obvious they’re trying to contribute, I’ll interject the talker (between thoughts, not interrupting) and ask the player being talked over what they’d like to do.

Now if it’s a shy player rather than one being talked over I might instead quietly ask them privately instead, then pipe up towards the GM with “hey, they say they’d like to do this” that way they’re not sitting there with an uncomfortable spotlight on them