1987 Pontiac Fiero does not shift into 4th gear

Define "easy" :) .

On the Fiero it is easiest for me to drop entire cradle, 4 bolts hold cradle to body.
You can disconnect ECM from console, push wires through bulkhead, disconnect C500 connector (next to battery) disconnect parking brake cable, hoses, strut bolts (3 small ones), and then raise rear high enough the entire assy will come out bottom (put a skid under there.

If you need any replacement parts go to fierostore.com.

Having said all that, check the shift and select cables first, they maybe loose/broke.