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Hello and welcome to just answer! There is actually a special tool to do this, and its very inexpensive. I have tried once to do it without the tool using long screwdrivers to try and pry it back in and I almost seriously injured myself, because that spring is very powerful so I would never do it again without the tool!
They are all over the Internet, including ebay, here is one example:
Many parts stores like NAPA and Auto Zone sell this as well. You may want to print out a picture and take it with you, to help ID the tool.
You simply open it as far as the door space will allow, insert it into the spring and use a wrench to close the tool, which compresses the spring. Then you can safely slide the spring out and when done, slide it back in and release the tool.