You would need to set up a custom circuit using some additional resistors, wires, and a plug to create the necessary charging point.
Do not bother with or otherwise mess with modifications. May end badly for charger and/or device.
Just get and use a low end charger. Low voltage, low amperage. Older USB (1.0) port for example.
An old USB hub should work. Just check specifications.
Even if the phone can handle quick charging that does not mean it will demand and do so.
It should charge at the slower rate if that is what is provided.
The following link will provide some background information:
https://www.digitaltrends.com/mobile/how-does-fast-charging-work/
However, to address your question, simply google "how to make a USB phone charger".
You will find quite a number of links, images, videos, and circuit diagrams with the necessary information.
Do be aware that some of those circuits are to boost into quick charging. The opposite of what you wish to do.
So you will need to read carefully and look for an older circuit that is designed for a slower charging rate.