Download a pic of Fabian Cancellara. Take a pic of yourself in a similar stance, so you can see the angles of your torso and arms. Attempt to emulate the fit as best you can while not sacrificing your power, or it being excruciating to hold.
In general, if you are trying to use a road bike for TT, you’ll probably need to move the seat forward, adjust the bars so that your arm angle is close to 90 degrees (sometimes a tad bit less, but never more…you don’t want your upper arms angled away from your chest as if you are leaning forward), and you may need to raise the seat a bit, but just use the typical road bike guidance for seat height or make sure that when your crank is at 6:00 and you are unclipped, that when you rest your heel on the top of the cleat, your leg is straight, not bent, or not over-extended to that your hip has to dip down… Then adjust your stack (height of bars) so that you can hold that position with your back as flat as possible. This will depend on your flexibility and ability to breath correctly, and the personal morphology of your chest and torso, so you may need to experiment. And you may need to alter the length of your bars as you do this to maintain that 90 degree arm angle.
I’ve set up my own TT bike before, to the point to where a professional fitter made only slight adjustments…we’re talking millimeters and not that big of a deal, so you can make the gross or macro changes on your own to get directionally in the right fit. It’s not rocket science, like many make it out to be, and bike fitters aren’t always right, because their guidelines and formulas do not always consider individual nuances or peculiarities, or how you actually ride on the road or in a race.