To edit your session on Floor, go to your stage and you will get an option (three dots) on right top of each session. Click on that and you can alter the information from there.
In case, you are already on a session that you want to edit then just click on Room Settings from bottom right and proceed modifying the information from there
Kindly refer to the GIF image below:
Note:
To edit the Session Name, just hover your cursor over the name and click to edit.
You may select the sessions also from the drop down highlighted above.