You can't really increase the GPU power limit on those. They don't have the cooling to support higher power draws.
Best thing to do is clean the fans, get all the dust out of the heatsinks, repaste it if you know what you're doing. If you don't know what you're doing either skip the repasting or make sure you've watched several videos covering repasting, common laptop ribbon cables and fan connectors. Laptops are easy to break without it even being obvious that you've destroyed them.
It does at least look realy easy to get into; newer laptops are always horrible plastic clips that you need to careful not to snap.
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