If you left it in gear when you unscrewed it you'll have to
either put it back in in that gear or you'll have to put the
transmission in neutral.

I was once driving my 144 along and the gear shifter came
out while I was downshifting. It was a bit disorienting to
have the shifter in my lap... I pulled over and shifted the
transmission into neutral and popped the shifter back into
place. There should be 6 little thingys where 2 move back and
forth together at a time. Just make sure that each one is
in the middle of it's travel, so everything is lined up.
That's neutral.
chris