There are three (generalized) ways to achieve your goal:
To manually adjust the indent on the left, you can use << to shift to the left once (repeat s . To get the desired level of indentation).
If you are already in insert mode, Ctrl + d will shift the current line to the left.
Indent automatically using = =
However, given your initial description of being in column 1 and wanting a
match with the others, I probably would just use d t a to delete to the first a.
edit: as Tim Pot notes, d w is a more efficient way to remove a space in the first character. I'm not sure what exactly you are trying to execute from your description (i.e. just trying to remove the empty space or all characters before the start of a
?)
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