If some door is not lock from the remote key this is a Guide to make first a Diagnosis and repair it.
All the locks have the same mechanism, they differ only if it is left right or the back door.
I will not describe how the doors lock Removal because there Guides who describe it :) :
https://www.fiatforum.com/grande-punto-guides/238842-drivers-door-lock-replacement-repair.html

You will need
a set of Torx drivers
Screwdriver & allen set (to remove the door panel.)
a dremel with a cutting wheel.

After remove the door lock mechanism you you can see the 6 pin connector.
The photo below is the 2 contacts which control the remote locking motor.
You can connect carefully 12 volts to τo hear the sound and vibration. polarity is not important if you redo lock it unlocks.

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If the motor is running the problem located somewhere else, Usually in the door wiring loom, i have seen many cut wire between the door and the body inside the rubber.

If the motor no working you must cut with a Dremel as you see with red line in photo and remove the torx screw.

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Carefully remove the motor, do not damage the plastic gear, use a small screwdriver.
As you will see, there are two contacts in the plastic (red arrows in photo) that give a 12v to the motor, You need to clean it, i use a contact cleaner but a alcohol is enough.

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Also you need to clean the contacts back on the motor, a trick is to use a needle to make the pins springs harder.

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Put the motor carefully back, now before you close it check if the motor working good using the door connector as you seen in this video.


Hope this helps:)