you do not have to buy that exact brand (bourns) the important thing, is to be multiturn and blue, with the metallic screw. they are common in EVERY electronics shop. bet you will find around your place.
if you want to go with the trimpot method, just follow these steps:
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hook up pressure sensor gnd to arduino gnd (common gnd)
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hook up arduino gnd and sensor 5 volt (here will come the pressure sensor output, after we done with the calibration) to the 2 side pins of the trimpot (doesn’t matter which is which side, but after this you should mark the gnd pin side on trimpot with a black marker)
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set dmm to dc voltage measurement
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digital multi meter (dmm) gnd goes to arduino gnd, and multimeter input to trimpot middle pin (called viper)
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now turn the trimpot screw until you will get around 3.0v on the viper
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hook up wiper to the arduino analog pin, and serial print the analog pin raw value to the display (in a new sketch, just for testing). now fine tune the trimpot until you get 1023 on the screen
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map the arduino raw value to 0 - 5.0v, and serial print
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now the voltage divider is calibrated, you can replace the 5v pin with the pressure sensor output
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you should double check the values again with dmm on sensor output and gnd, compare with the voltage indicated by the arduino
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probably, in your main sketch, you will need psi instead of voltage. so, you should map the raw values according to the pressure sensor datasheet (i do not know what sensor are you using)
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that’s all