Easy Installer should “just work” with Samsung S7.
The manual Command line install instructions (in addition to Easy Installer) are found linked from this page https://doc.e.foundation/devices/herolte.
/e/OS does not expect or require rooting before install.
You might just double check that you definitely have one on the supported models referenced above
Models Supported
SM-G930F
SM-G930FD
SM-G930S
SM-G930K
SM-G930L
SM-G930W8
Other models are not supported
If you ran Easy Installer and it failed, maybe you have run into an issue mentioned below and / or you should be able to find the log following the guidance.
Feel free to share the log here.
Edit A frequent cause of Easy Installer failure for Samsung users is mentioned here:
Also covered here Your first boot into TWRP.