I agree, I would not flush.
If old fluid looks OK just drain, remove pan and clean, replace filter and fill.
If it does look bad, drain fill. Remove return line from transmission cooler and put it a quart glass jar inside a bucket/oil drain pan. Start engine and run until 2 quarts or so are in the bucket. Refill transmission. Repeat until new/clean fluid comes out (easy to see in the glass jar). This replaces almost all the fluid, but does not "knock loose" any contaminants.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240