Need help setting up the Galaxy Watch Designer

I installed java but the galaxy watch Designer Installer still gives me the error saying that it is not installed.

Can someone help me?

Sure, It is fully documented HERE but it is basically one of these things.
You installed the x86 version of JRE instead of the 64 bit version or you already have the x86 version and the path still points to that.
I noticed after the last Java update my path was wrong, this may be the problem you are seeing. You can change the path in your environmental variables or you can uninstall all Java SE versions and start again. Restarting your computer after removing Java SE and after reinstalling it before launching the GWD installer.

Hope this helps,
Samsung Developer Program

Likely your answer: Samsung’s documentation is wrong. You can’t use any version of Java. It has to be Java SE Development Kit 8u201.exe. Newer versio aren’t compatible yet. Be sure you uninstall any other installed versions of Java.

We recommend Java 8 because it is the last publicly available version. However, unlike Tizen Studio which does not work with versions newer than Java, Galaxy Watch Designer has been tested with newer versions of Java JRE.
Also note that pointing to the Java jre in the JDK may not work I’ve had issues with that.

Samsung Developer Program