Meaning of It did not help that

I am reading the book 'Shoe Dog' by Phil Knight'. There is a paragraph in this book which starts with the following sentence:

It didn't help that, when I wasn't a foot soldier in Hayes's Army, I was still serving in the Reserves. (A seven year commitment.)

I want to know what is he referring to by the phrase "it didn't help that".
What is the correct meaning of "it didn't help that"?
Moreover, what does "a foot soldier" as the person (Hayes) is an accountant in the book.

I have not read the book which you are referring to, so perhaps some context which is relevant is missed to me. In general English, however, the phrase "It did not help that X" is usually used to express than an already negative event is further amplified by X. For example

The elevator in my apartment was broken. It did not help that my limp had only gotten worse.

Here, the narrator expresses their frustration that the elevator is broken implying that they must use the stairs - this is the negative event. The negative event is further amplified by the fact the narrator has a limp, making it even less convenient for them to use the stairs; hence, "it did not help that my limp had gotten worse."

It didn't help that, when I wasn't a foot soldier in Hayes's Army, I was still serving in the Reserves.

The comma-separated phrase "when ... Army" is a "parenthetical phrase" -- it adds information which, while perhaps necessary for comprehension, is not needed to have a "correct" sentence.

So analyze "It didn't help that I was still serving in the Reserves". "It didn't help" is the syntactic "meat" of the sentence, and "that ... Reserves" is a conjunctive clause (may be called other things, depending on your religion) that identifies what "It" means.

So "It" is the subject "did not help" is the verb, and "I was still serving in the Reserves" tells us what "It" means.

"Reserves", especially when capitalized, would be taken to mean "US Army Reserves", people who work "normal" jobs but who can be "called up" on short notice to serve in the military. They generally must attend training sessions at regular intervals, somewhat disrupting their "normal" lives.

It's difficult to say with any certainty but I would interpret "Hayes's Army" to mean that "Hayes" is a business manager who expects military-like obedience and subservience from his underlings. "Foot soldier" implies that our narrator was in the lower ranks of Hayes's organization.