in the file tab go to > import> from financial institution > enter abd select Schwab and proceed as directed. after you agree to imports and close the windows you should see a list of forms being imported. If your other account isn't there contact Schwab to see if accounts can be linked.
However, I think all accounts using the same login should appear.
if you're using online, It has to be premier or above to allow import and you should be able to do that once you reach the interest and dividend section.