yeah, I had the same issues at the beginning. make sure that you're really using a bigger noozle than the one for the phones or the M92T36 ic on the NS so that you can apply the heat on a wider area. I do it always like this:
1. Apply some flux
2. Heat up the CPU/APU with about 400° until the solder gets soft (this usually takes 3-4min and I need this temperature with my hot air station since I haven't got a board to preheat the NS mainboard)
3. Use this tool (
https://de.aliexpress.com/item/32846496929.html?spm=a2g0s.9042311.0.0.55134c4d8lUEDD) or anything similar to lift the CPU GENTLY from the board
but be very carefull when you lift the CPU so that you don't damage any pads on the mainboard or on the CPU. afterwards I do a reballing with the stencil and then you can easily put it back on the mainboard. So far I wasn't able to do a reflow since the factory solder needs really high temperatures to get soft and therefore I do a reballing always. maybe
@FXDX has a better idea? ;-)