Try a custom number format:
h:mm AM/PM
Select the time cells (your Column A or B).
Press ⌘ + 1 to open Format Cells.
Go to Number → Custom (at the bottom of the list).
In the Type field, enter:
h:mm AM/PM
Click OK.
This removes the “:00” seconds while still keeping AM/PM.
I gather you typed the original one manually, or Excel interpreted it as a time without seconds (e.g., you typed 2:43 PM). Excel automatically formats typed times using the shortest matching format, which is probably why it lost the seconds.
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hth
Marcin