Getting To The Retaining Screw(s) Of The Paddle
REMOVE ALL POWER FROM THE MACHINE. UNPLUG FROM ELECTRICAL SOURCE.
The sump hose is the thick hose that will run from the very bottom of the drum to the the pump.
You need to take this hose off to gain access, again, make sure you have removed all power from the machine as you could go near power carrying components.
Once the sump hose is off you can see the drum paddle retaining screw through the hole. Pull the washing machine out and tip it back so that it rests at about a 45˚ or so angle. Makes sure the washing machine is secure and cannot move so that it is safe to work on from underneath or, get someone to hold it for you so it doesn't tip over onto your head or hands.
Now you can access from below in most washing machines, especially the cheaper ones as it costs too much to put a base on the machine.
The sump hose may be sealed into place so you might need some sealant such as silicone sealant to reseal the hose once you are finished replacing the paddle.
Once that hose is off you should be able to see inside and see the retaining screw, bear in mind that these will often be Torx type screws. Undo that and the paddle should be able to be pushed forward or back depending on the fitting in that particular washing machine model, and the drum paddle should just pop off. Unless it's one of the really hard ones.
The rear screw, if you have one, you have to take off the top breather hose at the top of the washing machine's outer drum.
Obviously you will need to rotate the drum to access the second screw if it has 2 screws.
To refit the new drum paddle which you have, simply do the process in reverse.
Your image shows 1 screw, but the paddle looks like it may use 2. Until you take the paddle off, you may not know for sure.
Also it seems that there are part numbers manufactured into the top of some paddles. If so, it would be close to the holes in the front part of the paddle.
If you can find the part numbers, you might be able to find the actual part online for an image then determine how many screws are in it. It could be easier than this and just be one screw holding it on from the top...where is a good guess as it could be any number of the holes.