You can use

<%= link_to "return", request.referrer %>

to get to the previous page, but it is better to use

<%= link_to "return", :back %>

because the :back thing provides the following code logic:

request.referrer || "javascript:history.back()"

<%= link_to "return", request.referrer %>
# Will generate an absolute url to origin page.
# If no previous page, will be an url to CURRENT page
# The javascript leverages in-browser navigation.
# If no previous page, will be link to something like "New tab"