Solid Hardwood, Engineered and Laminate Flooring - Fixing voids and soft spots

I installed a new hardwood floor at my place recently. It's a floating engineered wood floor over concrete slab. I also used a sound+moisture barrier between the wood and the concrete.

I realize the concrete subfloor should be pretty flat in order to prevent voids, soft spots, or squeaking. But being an amateur, I couldn't really tell that the floor was uneven before I started -- I tried to measure the flatness to spec, but it seemed pretty flat to me at the time.

I guess I must have missed a few spots, but right now there are a few spots that feel "soft". It's not too bad, but I'd definitely prefer if it felt more solid, especially since the most severe spot was in a very high traffic area.

Is there a simple way to fix this, without taking out the floor? I don't really have the budget to get it fixed professionally either...

I found that for glue-down engineered floors, there is a product called DriTac -- a kit that lets you drill a hole into the wood and fill it with some adhesive using a syringe. Would something like this work for my floating floor?

That product is used for gluedown wood, not floating floors. The only way to fix your issue is to take the floor up and flatten the subfloor.

Im having the same problem with my flooring. a few soft spots in high traffic areas. There must be some way to improve the low spot without taking up the whole floor.

Ive considered using expanding foam but worried it might actually lift up the floor instead of expanding across the floor. Ive considered drilling a small hole and inserting dry sand to fill the low spot. My concerns is that it would be above the vapor barrier and might make some noise when stepping on it. also, the hole would have to be fairly large to get the sand under it. Surely someone knows of a way.

The nice thing here is that floating floors come up very easy, so it looks like you get a second chance to do the job right this time. I suggest marking out the hollow spots and taking a picture so you can reference it when you are doing the floor prep.