Gardenias are extremely temperamental and will yellow out leaves or drop flower buds at a moment's notice for any reason. Water issues or changes in sunlight caused by moving the plant from the plant nursery to the home are enough to do that.

The plant has flower buds, unopened. So, I would wait until the blooms have opened and if placed outside, then I would wait until lower Fall temperatures arrive. That way, you may get to enjoy those unopened flower buds that I see in the picture. If you start moving it around much or worse, fiddling with the roots, there is a good chance that the gardenia will abort the buds and they will fall... or the buds turn black and die off. And produce those dreaded yellow leaves.

Thank you ! Can I put in indoor facing a sunny window?

Yes, I had one getting morning sun some time ago. Here is more info:

https://m.wikihow.com/Care-for-Gardenias

U still have it ? Is your gardenia doing ok ?

Where are you located? If you have a spot outside that gets morning to early afternoon sun I would put it outside. Gardenias do really well outside if you can find a spot that doesn’t get too much harsh afternoon sun. If you gardenia is doing well now and you’re not having to water everyday to keep it from drying out (a symptom of being very pot bound) I would wait until fall to repot after it has bloomed. Often growers will allow the gardenias to become very potbound to force a lot of buds for retail sale so it will most likely need to be at least potted up to a 10” container (not too much bigger). Where you’re located will dictate the timing. Lastly the black nursery pot will heat up too much if placed in full sun. If you can put it in a lighter colored pot it will help to keep the roots cooler, but make sure it drains or take it out before you water.