The "Decosonic" convection cooker was made by a company in China several years ago and marketed under about a dozen different names. It's amazing how many people pick these up at garage or yard sales and they don't have the instructions. It seems the paper the instructions booklet was printed on was biodegradable in 1 year - or they were only sold to people who agreed to throw the instructions away before "re-selling" them!
There are literally hundreds of people looking for these instructions on the Internet.
You might try this site - its the instructions for the Galloping Gourmet trademark version of this product. According to Jennalynn it's the same as the Decosonic manual. It ain't pretty, but it's free!
We did have a member who had a Decosonic manual - and was willing to sell copies of them for copy charges and postage ($4). Don't know if he is still around or not ... but you might try the email link in this post.
After Googling the Decosonic, I was reminded about a question asked here a short while ago about the Nu-Wave and Flavor Wave ovens. Look here for the thread
The Decosonic looks very much like those appliances. Maybe the instructions for those would be applicable to the Decosonic.
Perhaps this would be another avenue for you to search. It's possible you could download their instruction manuals. I don't know because I'm not familiar with any of these 3 appliances. Just something I thought I'd throw out there for you.