The problem is that you haven't given mutate() the data frame that you're working with.
data %>%
mutate(**your code here**)
should work. In the future it's much easier to help you troubleshoot if you include a self-contained reprex (short for reproducible example). It will help us help you if we can be sure we're all working with/looking at the same stuff. And is much easier to read than looking at screenshots.
There's a nice FAQ on how to do a minimal reprex for beginners, below:
What to do if you run into clipboard problems
If you run into problems with access to your clipboard, you can specify an outfile for the reprex, and then copy and paste the contents into the forum.
reprex::reprex(input = "fruits_stringdist.R", outfile = "fruits_stringdist.md")
For pointers specific to the community site, check out the reprex FAQ.