Hi,
Here is how to do it:
Make a bleach/water solution--you only need about 1 part bleach to 9 parts water so you could put a splash of bleach in a bowl of water. (watch out that you don't get any bleach on your clothes!).
Swish the plants around in it for a few minutes then rinse, rinse and rinse. For a final rinse, soak them a bit in a container of water with water conditioner added--it will get rid of any residue of chlorine (which is bleach).
Then you can safely put the plants in your tank.