In a nutshell, the turnaround is the root chord of the 12 bar blues for a bar, then moving to the V chord a beat into the second bar. However, it is the chromatic movement that gives it it's true nature. You stay on the root chord root note (in our example this is A) and then chromatically move downwards once step at a time, resolving back to the root chord for the start of the 2nd bar, then moving to the V chord. You will see this clearly on the chord-based turnaround. For the lead-based turnaround use the A major pentatonic, A minor pentatonic and A dominant 7th arpeggio. Then, in the second bar, resolve to the V chord root. Those scales are shown below:
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