How to get a synthetic cork back in a wine bottle?

There is no trick, it just won't work. Synthetic corks are popular as replacements to cork not only because they are cheaper, but more effective at preserving wine as they don't dry out, and they expand more in the neck keeping a tighter seal. This makes it more difficult, if not impossible, to get them back in.

The simple and easy solution is to buy re-usable bottle stoppers. There are many different types, I prefer the ones which have a lever or button you push down to expand the stopper as they are best at preventing spills and leaks. There are vacuum sealers as well, however IMHO they're gimmicks and don't improve the storage of wine.

One method that has worked for me if you desperately need to use that cork again is to shave the end with a knife to create a taper so that it will slide into the opening of the bottle and then with the pressure of your hand you can squeeze it down in.

I always keep a set of reusable rubber corks around though for this very problem. They're cheap, come in sets of 2-4 and will fit pretty much any bottle.

I can sometimes get them back in by flipping them over and using the corkscrew end.

But if you can, you're better off using one of those rubber stoppers with a vacuum pump (e.g. "vacu-vin"). It will remove a lot of the air, preventing the wine from oxidizing as much.

Why not just use a old "Real Cork" cork... You should still have one around the house... I save my corks from whiskey bottles, as the have a nice top, and almost always fit into the neck of any wine bottle.

Flip it over and insert the dry end back in the bottle. I do it all the time!

Saw a bit of diameter off the cork with a bread knife and happily plug it back in (it may not seal it completely but it'll do overnight)

Why not expand the wine bottle head using heat then fit the cork back in maybe that should work

I just tried it and got it back in. Put the cork in at a 30-45 degree angle and keep applying pressure. This works best if you can sit down with your feet under you butt and keep the bottle tight between your thighs. Apply pressure and take a butter knife and keep working the edges in. Once in just put your weight on the cork and ta da!

I shaved the plastic rind off with a scissors, squeezed it in as far as I could with my hands, then put the hard plastic bottom of a bottle of ibuprofen on top of the cork and pressed down. I imagine any kind of grippable, flat and hard thing would work. The ibuprofen bottle made it much easier to apply force once the cork was in a workable position.

When I have tried and am alone with no muscle, I have tried every trick internet search gives.... not even warm/hot water worked for me with plastic corks in large champagne bottles... what worked at end of day even after going to buy a whole other bottle and its cork also not giving way.... butter knife!

Just keep prying under cork with a butter knife (it may bend- don't use one that may be missed if you bend it!). Just continue to pry each side you can get it up into the cork and sure enough pried way to which I could then pull off the cork!