Can’t fill cavities in mesh

I’m pretty new to 3d modeling, not just this app. I’ve been having trouble with these cavities that have appeared in the mesh, and can’t seem fill them. Not sure what tool I used to make the holes since I just barely noticed them.

If just regular smooth isn’t working well enough. Try it with dynamic topology and set it to uniformisation or decimation. Or, if it’s recessed too far (which doesn’t seem to be the case) you can always fill it with some geometry and voxel merge any hole away.

Thanks, the adding geometry/voxel mesh method worked pretty well.

Otherwise the flattening tool (with the « fill » option enabled) can help as well.