According to :
Hi,
I just moved to a new house and the dryer hookup box has two cables
coming into it. (i.e. there are 2black, 2white(neutural), and 2 ground
wires) . Both of the cables have 30amp breaker each. Can anyone give me
words of advice how to make the connections for a 4 prong hookup.
Thank you in advance

This was wired incorrectly from the get-go. It looks as if the
person who used it used two separate 120V (with ground) circuits
to make one 240V one, and promptly didn't bother using the ground.

Code violation amongst other things (separate breakers, multiple cables
for the same circuit). Further, I have my doubts whether
the cable is in fact properly rated for the ampacity you're pulling
from it - if they were stupid enough to wire it the way you have
it now, I wouldn't put it past them to use undersized wire _too_.

Without a very close look at the circuit (eg: wire size, where
the breakers are, tiebars etc), I recommend you call in an electrician
to figure this mess out. I'm not going to tell you how to make the
existing double-cable mess "work". Because it's dangerous, perhaps
_very_ dangerous, and they probably screwed it up in other ways that
you haven't realized yet.

Correctly done for a modern code 4 prong hookup, this circuit _should_
have a single 10gauge 4 conductor cable (black, red, white and bare),
connected to a dual breaker (two breakers connected together with
a tiebar). Which means pulling a new cable.

_If_ the existing cable size was right, and you replaced that breaker
with a dual, you could abandon one of the cables and make it a 3 wire
connection. But I don't recommend that, despite the fact that it's
still code legal (renovation grandfathering) in the US.

It ain't legal, period, in Canada. Hasn't been since at least
WWII. If you try to install a dryer onto an existing circuit,
it MUST be converted to 4-wire. No exceptions whatsoever.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.