You will need 9 puzzle pieces to fully rebuild a bridge. You will earn these from various quests, or you can go to the shop where Samir is, head to the right when you get inside and they are up for sale at 2500 gems each should you have gems to burn, which is likely if you’ve been harvesting your crops, completing quests and selling any items you get your hands on.
Once you have 9 pieces, approach the sign post next to the bridge, press
to select it, then press
9 times to fix the bridge. The achievement will unlock once the timer runs down to 0 seconds.