Hard to know without seeing or feeling the bracelet, but I’d trust the AD on this. They’ve handled thousands of watches, I’d imagine, and have no reason to lie to you about this.
In my experience bracelets definitely do loosen up over time as springbars, pins and sleeves bend slightly. (After years of extended use the “give” in the bracelet can get problematic, at which point you or a watchmaker can replace those connective bits.)
That said, this isn’t something that will just happen on its own in a drawer—need to wear the watch regularly.
I’m guessing a couple weeks of daily wear and you’ll be fine.
I would not recommend trying any forceable or chemical “solution.” Just let it happen au natural.
