Open create a new world window or edit an existing one. If you want to use experimental features in your existing world, it's highly recommended that you create a copy of it before doing so.
Scroll down a bit and you will find the option Wild Update, activate it.
You will get a warning window, click Activate Experiments.
Now you will be able to meet frogs and tadpoles in the swamp biome. The spawn eggs also available in the creative inventory.
This also works with the release version of Meinkraft 1.18.10 and above.