Undervolt & limit max frequency of GPU via MSI afterburner's voltage curve editor. Check video by Bob of all trades on how to use it.
I hope you have cleaned the fans & heatsink off dust. Maybe your heatsink ahs warped a bit over years of usage, nothing much can be done. Also, if gap between outer heatsink above CPU/GPU & bottom plate isn't much + bottom plate is metal, then fit a thermal pad in between to make bottom plate a passive heatsink. Clean the mesh on bottom plate of laptop. I also hope you are using a cooling pad.
Deepcool Multicore X6 is what I use, costs 1.7k.