Help with removing water pump

Hello all, first, full disclosure, I'm a newbie to gaming PCs and water-cooled PCs. I bought this PC from a gamer and I was using it to upscale video with AI software. It worked great for about 4 months and one day it stopped working. I contacted the person who sold it and he said it might be the water pump (D5) and that I should try to drain the coolant, remove the reservoir and try to clean the pump. He told me where was the drain screw, unfortunately I had to leave for several weeks and lost contact with him. Nevertheless, I am hoping someone can walk me through draining the coolant and removing the reservoir and pump to clean it, I have seen the video on YouTube on how to fix it but I'm stuck on how to remove the coolant since there is no valve and I don't have any materials like a hose, connector, jumper etc. what should I get/buy to start the process of draining the coolant and then how do I remove this reservoir to remove the pump. I noticed some white residue on the bottom of the hoses, what is that sediment? Any assistance is much appreciated.