How do I fix the ice build up in the bottom of my freezer hoe do I remove the basket and drawer rails

Turn off unit. Look at rear cover and see how to remove it and take it off. I am sure you can see some way to do it. Once removed let it sit long enough to thaw out. You will see coils and a drain under it. Pour hot water down drain to clear out. You can also use a hair drier to help it thaw. These drains get clogged with food residue. Look under unit and clean out coils, too. You may need to remove front and rear covers to get at the coils. Blow them out with compressed air and/or wash off with spray of water from water hose. It's really not that complicated; you just have to use your eyes. DrTom4444