This maybe an easy question but I am stumped.

If I click in a cell and hit F2 and enter then the formatting of my date
field is amended somehow.

How can I apply the F2 + enter to a large number of cells all at the same
time?

For some date fields in my spreadsheet when changed to general format,
become a number, others remain as dates - why is this and how do I get them
all to be the same format (other than the F2 method I have discovered)