Ruby - Adding more than one includes on an if statement

I have the following code which works fine

if user_input.include? "s"
    user_input.gsub!(/s/ "th")
else
    print "Nothing to change"
end

But when I want to add another include like so it does not recognize the elsif How do I add these includes together?

if user_input.include? "s"
    user_input.gsub!(/s/ "th")
if user_input.include? "cee"
    user_input.gsub!(/cee/ "th")
else
    print "Nothing to change"
end