Android does not have a swap partition as it's delivrred. RAM expander just tries to create one. Somehow it failed in the process. It may or may not have actually created the swap partition. You'll have to check to see.
Trying to use swap in Android Is, IMHO, a waste of time. There's legitimate reasons why Android has no swap file by default. If RAM Expander has an 'Undo' function use it.
Otherwise, to get rid of the error message try uninstalling RAM Expander. Do it this way:
Settings > Apps > Select RAM Expander > Force stop > Clear cache > Clear data > Uninstall.