If you are going to do games you should get familiar with reading and understanding lisence agreements.
According to the asset store lisence you can only use the assets as part of electronic games and interactive media. There is no mention of the engine you use at all. Which means it’s legal to use an asset in whatever engine you like, as long as you only distribute it in an electronic game or interactive media.
Yeah as BoredMormon said. As you’ve bought the asset, you can do effectively anything with it as you’ve bought the rights to use as you wish, including using in another engine.