Hey @Armin, welcome to the site.
You have not provided enough details here for us to help you. Please read through this post on how to create questions on this site and then update your post with more details:
https://discourse.threejs.org/t/please-read-this-before-posting-a-question/24/2
In particular, you need to always include sample code that demonstrates your issue. We usually cannot help you without that.