Simona: Maybe this link will help
if you want the plant to continue to grow after Christmas, treat it like any house plant. Make sure you have good drainage and light. Most people kill their plants by over watering. I perfer my plants to be in a clay pot with a drainage hole in the bottom, some gravel or marbles at the bottom of the pot to allow drainage . I only water when the dirt is dry and then I give it a good watering (some water coming out of the drainage hole onto the plate under the plant) .
It’s going to depend on the type of dirt—some hold more moisture and other hold less. If you water too often and don’t have good drainage, you will get root rot and it will kill the plant. If you water too little, the leaves will droop but will usually perk up once you give it water.
I had the same poinsettia for over 10 years until I got a new kitten who kept knocking it over.
A friend of mine got her poinsettia to bloom again so you may find her tips helpful
Here's an article on the topic: https://homegardenjoy.com/site/2017/12/how-to-get-a-poinsettia-to-bloom.html