In your file, select the cells A1:C7
Press F5 (function key) on the keyboard,

click Special…
choose Blanks, click OK
Now don't touch anything except:
press the = sign on the keyboard, followed by the up-arrow (cursor key) then
hold down the Ctrl key and briefly press the Enter key.
(Your blanks should be populated now)
Convert the formulae to plain values by copy/paste-special|Values in situ.