In 1948. Everyone who participated in that is dead or will soon be.
Wars happen, conquest of land too. Some win, some lose, many die, people are moved, treaties are signed and borders established. That's how it worked for millenia and how it still works today.
Or should all white Americans go back to Europe, and all arabs in Africa back to the arab peninsula, how far back do you want to roll history back?
You may not like it, I don't either, but reality doesn't give a shit about what we think.
There was a war, israel won it, they took the land, and Palestinians don't have and won't have the means to wrestle it back. That's reality.
At one point, you lost, you should cut your losses and try to get the least worse deal with the last bad cards you have in hands.
But Palestine acts like the addicted gambler who bets ever more in hope to win back what he lost, while crying to other people that the casino should give him back everything he lost. As if that would happen. Except in a casino, you have 49.5% chance of winning. Here the bet is always losing, and israel is the croupier that is all too happy to incite the gambling, knowing that every new bet will get them more land.
Imagine if germany was constantly crying about the parts of its old empire that it lost during the 2 world wars while bombing Poland every other week. It would still be under the allies rule, maybe not unlike Palestine is now. Instead they cut their losses, accepted their new borders, the land they lost and the reparations they had to pay and now they regained their sovereignty and became a successful country.
History happens, cut your losses, sign peace and work for a better future.