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use a multiturn potensiometer (or resistor network) to generate voltage for one input. This voltage should be equal to loadcell output at no load.
The circuit you want is the classic Wheatstone bridge. A 3-wire sensor is just one arm of the bridge,
so you need a 2nd arm made of two precision resistors (and optional trimmer in the centre).
One of the arms goes to IN+, the other to IN-, they share the power connections.
Note the need for precision resistors, I'd recommend 1% or even 0.1% metal film types.
Perhaps two 1k metal film resistors and a 47 ohm trimmer in the centre, cermet type, like this:
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+PWR, -PWR
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The gain of your amplifier will need adjusting to a lower value if its too high...
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Connecting a large resistor between IN+ and IN- could help to reduce sensitivity. I would try a 100k but it is only a wild guess.