If this question is about an automatic transmission, there is no drain bolt, you must remove the pan, which will not only allow you to drain the fluid, but also change the filter. You will have to replace the pan gasket. All the items that you need are in a kit, gasket & filter.
in my 88 astro van I had to completely break out the back handle to first get the door open then I was able to remove interior door cover to do thr replacement. in my 99 asto van I was able to remove the interior cover to open the door then replace the handle.
A V8 engine is put in a Chevy Astro van by removing the existing engine and removing all unused accessories. The engine can then be put into place, bolted to the transmission, and everything hooked up.