On this page of the trophy guide for Resident Evil Village, you will find information on how to unlock the Repairer achievement. You get it for combining treasures into their complete form.
Treasures are divided into two groups - those that are single objects and those that are parts of sets. To get the achievement, you must find items from the latter group.
Treasures that can be combined with others have Combinable written in the description. In addition, you can see the number of parts - the example in the picture shows two. Don't sell the parts of the sets to Duke. Instead, continue exploring until you find all the treasures from a given set.
An example of an easy set to complete is the Wooden Animal treasure.
You can find the first Wooden Animal (Body) component in the hut presented in the above pictures. You can get it during your second visit to the village or later (after returning from the castle).
The second component Wooden Animal (Head) is in the village's well presented in the picture. You need a Work Wheel for this - we described how to get this item on The well - how to start the mechanism? page.
Open the inventory and go to the Treasure tab. Select any of the treasures described above and choose Combine.
Combining the two treasures into the Wooden Goat will unlock the trophy.