Dip under hardwood floor

[m0t]

I fitted a hardwood (strand woven bamboo) floor last year on top of concrete which had a self levelling compound applied by a former builder.

It turns out the floor isn't quite level and there is a dip under one plank. This has caused the board to crack (unnoticable unless standing on it).

The floor is glued together and would be massive job to replace. I have seen people talking about injecting stuff under the boards. What's the best way to go about doing this and what's the best thing to use?

 

[big-all]

ok my thoughts
do not use any foaming product on small dips
what size is the dip ??
my thoughts are wood glue pumped in every 200mm or so through a 3-5mm hole to say 30% fill the void and stand on the dip to form strings between the surfaces
this assumes around 5mm -8mm dip
anymore would require something like no nails of foaming pu glue but carefully controlled with walking on the area to pump under again 30% if no nails but around 10-15% if pu foaming glue with perhaps a plank or simillar weighed down to stop the area rising needs to be left in place for a few days