How do you raise the feed dog

There is a button with two "prongs" or wings. Rotate the prongs clockwise about a quarter turn, to face the square mark (Q in the diagram) then press it down. It will stay down. To raise the feed dogs, turn the prongs anticlockwise (to S in eh diagram) and it will pop up
https://www.manualslib.com/manual/1205574/Necchi-Automatic-Supernova-Ultra-Mark-2.html?page=7#manual

https://www.sewingpartsonline.com/instruction-manual-necchi-3204fb.aspx

If you raise the presser foot, set the stitch length to a 3 or higher, then slowly press the foot control, can you see the feed dogs rise, move backward, then drop and come forward again? If they are not moving, the feed dogs have seized. If they are moving but do not rise above the needle plate, then you have them disengaged.

If they are seized, resist the temptation to run the machine anymore until you can get it serviced. It could damage the motor causing more repair cost.

If they are disengaged (dropped), then you need to find the control lever or dial that engages them.

A lot of machines have a control knob/lever that raises and lowers the feed dogs. However, remember that when the control is activated, the feed dogs will not rise until the machine actually begins to stitch.

If the feed dogs do not rise, then there is most likely a problem and needs to be serviced.

I suspect the knob on the lower right hand side is the feed dog knob. The "knit" symbol is for the feed dog. One setting drops the feed dogs so you can move the fabric yourself, ie free motion quilting. The other setting raises the feed dogs so the machine will feed the fabric for you.

to find a manual, Search the internet:
Brand + Model + the word "Manual"
...

If you change the number of your stitch length it will automatically adjust the feed dogs. If it is still a problem then you will need it adjusted. Insure that your pressure foot is placing enough pressure that causes the feed dogs to pull the material forward. To adjust the feed dogs there are different ways to be adjusted. I wouldn't suggest you try to adjust the height of the feed dogs.

Manual is $14.99 from http://www.sewingpartsonline.com/instruction-manual-necchi-3204fb.aspx
Or $10 on ebay at
http://www.ebay.com/itm/Necchi-524-FB-Sewing-Machine-Original-Owners-Manual-/131339160836?pt=LH_DefaultDomain_0&hash=item1e946c8d04

the presser foot or what ever foot your sewing with does not feed the
fabric,, the feed dogs in the needle plate are what moves the fabric
to be sewed, the feet only hold the fabric against feed dog so the
machine can use the needle to sew the fabric.
if the fabric is not moving then the feed dogs have to be checked
can you see the feed dogs in the needle plate area are the up or
down?
do you have a manual for the machine?
a manual help to know where the feed dog lever is, I'm sending
you a link for a manual for the machine, so you can look for the feed
dog lever, if the feed dogs are up then there is something wrong
with the feed dogs & they need to be checked.
but if the feed dogs are down then look in the manual & see where
the feed dog lever is & put it in the up position & see if that brings
the feed dogs up to the sewing position, if the feed dogs do not
come up then the feed dogs need to be checked.

http://www.sewingpartsonline.com/instruction-manual-necchi-6015.aspx

the presser foot lever is either on the left side of the machine where face plate is or at the back of the of the machine on the left

If , you go to www.tias.com you wil be able to purchase a copy of a technicians book, the Sears Kenmore Sensor Sew 100 was the same machine, Necchi made it for them. Parts are going to be next to impossible to get. My motor is shot, but everything else is like brand new, boards etc. I bought the book and that is why I knew it was the motor. Sometimes, ebay will have one for sale, but they want too much. I am using mine as a doorstop, LOL, I paid $800 for it new in 19884. Good luck