Copying and pasting is fairly imprecise. I would suggest using the following menu item - Audio > Edit Audio > Timeshift Audio (ms). This brings up a window where you can enter the amount of milliseconds you want to shift the audio by.

To figure out what to enter here, if you want to shift by exactly one bar the math is as follows:
(60/Tempo) * 1000 * Beats per bar

So at 120bpm in 4/4 that would be (60/120) * 1000 * 4 = 2000
Or at 80bpm in 3/4 that would be (60/80) * 1000 * 3 = 2250

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