Andy,
Go to the regular Find/Change panel and then click the GREP tab — not the usual “Text” tab. Make sure both Find and Change text fields are empty, and there is no formatting in either. Those work the same as it does as in the regular Text change.
Type in the top (“Find”) field
^ +
— mind the gap! That is a single space in-between. Leave the bottom “Change” field blank. Now hit “Find” and check if it finds and highlights the first occurrence of a space at the start of a paragraph. If it does, hit “Change all” and duck.
The magic codes are
^ = Start of Paragraph. Sort of the same as “^p” in the regular Find/Change dialog, except that this is a *position* only, and it doesn’t ‘eat’ the paragraph return. Since it’s only a position and not an actual character, it also works when there is no Paragraph return ‘before’ the start of a paragraph.
(imagine a single space here) = The literal text to find. GREP uses lots and lots of special characters as commands (the ^ above is one of them) but a space is just a space.
+ = The previous command, group, or character, and then repeated as much as possible.
So this will look for *any* positive number of spaces at the start of a paragraph, be it 1 or 42 or any other number larger than 0. Replacing them with ‘nothing’ does exactly that: it deletes them.
How is this different from David’s suggestion? (Sorry David!) He suggests
^+?
where the ” command stands for ‘any kind of space’. That can be useful because apart from a single regular space, this also includes tabs, hard (unbreakable) spaces, and even en and em spaces; but *also* the hard return and the soft return. The latter may unintended wreak havoc on your document, as two consecutive hard returns are *also* seen as “start of a paragraph” (right after the first hard return) followed by “white space” — the next hard return. The next hard returns — any number of them — will also disappear!
Based on your image I understand there are only regular spaces at the start of paragraphs, and so my search expression is a bit safer.
For more information: IDSecrets has a page full of links to resources on GREP: https://creativepro.com/resources/grep