How do i recline the Peg perego Prima Papa high chair?

Here you go:
http://www.ebay.co.uk/itm/NEW-Prima-Pappa-Highchair-Cover-In-Medium-Brown-WIPEABLE-/231189872271?pt=Feeding&hash=item35d3fd7e8f

http://www.ebay.com/sch/i.html?_nkw=peg+perego+high+chair+covers

Here you go - direct from the Perego website:

http://us.pegperego.com/admin/archive/manuals/P.P.BEST_NA_FINA1001I88.pdf

You may be missing a piece. Take a look at the Prima Pappa manual from the Perego website. You can buy a new high chair harness if you are missing pieces.

http://us.pegperego.com/admin/archive/manuals/DINER_NA_FINA0802I60.pdf

Here you go:

http://www.karlisles.com.au/baby_repairs_spares/instruction_booklets/Peg%20Dondolino%202006.pdf

Is this what you mean?
http://www.momsjustknow.com/replacement-coverscushions.html

There is a lever under the front middle of the tray. Stand in front of your chair and reach under and squeeze it. You will be able to pull the tray completely off the chair, or out slightly to give the child more room. The seat also reclines back 4 positions so if your goal is to remove the child easier, that would help as well.

Check this manual out - It is from 2005-6 so it's closer to your model's year. Possibly you will find your answer there.
http://www.karlisles.com.au/baby_repairs_spares/instruction_booklets/Peg%20Dondolino%202006.pdf

How to turn in to a rocker

Here are a list of current cushions available for Perego Prima Pappa models. The correct cushion depends on the model you own.

http://www.momsjustknow.com/replacement-coverscushions.html