My guess is that outside trim is the type that pushes into a groove cut in the wood. As such, I would pull out the trim and seal the wood with epoxy
... otherwise for outdoor use water
will get in there and then swell the wood ruining the table.
The trim is readily available, or you could re-use what you have.... you may find when you reinstall it that it meets on the end... or not! If you replace it, let the table and new trim sit out in the environment
you intend to have it in. so any shrinkage or expansion occur prior to cutting. I would cut it in cold weather
rather than hot.
You could fill the gap with a hardening sealer like white 5200, or other type. Some sealers like 5200 will yellow slightly in the sun though.
When reinstalling the trim you could coat it all with sealant
, wiping the edges clean prior to hardening.