The White/Brown wire is only live when the engine is cranking so you could just connect it to the White/Yellow wire to give 12V at the coil when cranking,
BUT the normal coil feed will come back down the White/Yellow wire and may (probably will) keep the relay charged, and therefore the starter will stay engaged - not fun.
You can use a diode, which only allows current to pass in one direction i.e. to the coil, and not away from it.
Get one of these
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...and plug the White/Brown into one end, then onto another of these spades, connect a wire to the terminal on the starter motor. So now your trigger wire is still going to the starter in the same way, but has a connector in it.
Then plug one of these into the other spade..
1 x In-Line Schottky Barrier Rectifier Diode - Universal - 10A - 50V DC. It will only allow electric current to pass / flow in only one direction acting as a 1 way valve for electrical current, a blocking diode.
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The other end of the diode (Male spade) should connect to your White/Yellow wire. The electricity only flows in the direction of the arrow.
I hope that makes sense.
Trying not to be blunt, but if you're really that bad at electrics, it may be a good idea to have a fire extinguisher handy, or someone who is good at electrics.
And don't use scotch blocks