You have to import the VBO itself first. Once logged into Blue Prism, choose File > Import...:
From the resulting dialog, browse to the VBO folder within the directory in which Blue Prism was installed and open the file called BPA Object - MS Excel.xml. In most cases, the directory in question should be located at a path similar to C:\Program Files (x86)\Blue Prism Limited\Blue Prism Automate\VBO.
After you‘ve successfully imported the object, close and re-open whatever processes/objects you have open to see the MS Excel VBO option in your Action Stage configuration:
