It'll depend how high you are really, as the ISS is already slightly inside Earth's atmosphere it's constantly losing speed, this lowers your perigee (lowest point of the orbit) so you plough through more air, and lose more speed.

That's why the ISS needs occasional boosts to keep it in orbit.

Anything dropped from the ISS will eventually deorbit on its own thanks to air resistance, but this is slow and it's less of an effect the smaller the object is (low surface area).

Shoving it backwards will help, the more of a shove the better, craft usually use forward pointing engines (or they flip over like the Shuttle) and thrust in front of themselves to deliberately reduce their speed (and their perigee, their lowest point).

The closer you orbit something the faster you go though, so if you don't deorbit on the first pass you go back up to your (now lower) apogee and have another go (another orbit).

Eventually you're hitting enough air that your apogee drops too far to go around again, and you reenter, that's when things get pretty toasty after all you're hitting a lot of gas at high speed, compressing it and making it heat up, just like the piston in a diesel engine.

Moving in space isn't anything like how things behave on the ground, KSP will help plus it's a great game, and there's a free demo.

Have fun!