It was proven by Rosser, Yohe and Schoenfeld that the Riemann Hypothesis is true for the first 3,500,000 zeros and that they are all simple.
I’d be interested in reading their paper ‘Rigorous Computation and the Zeros of the Riemann Zeta-Function’ to see exactly how they used Turing’s method to prove this but I cannot locate it anywhere.
Where would I find this paper to read?
This appears in Volume 1 of the IFIP Congress 1968 proceedings. On WorldCat, this is here (though it looks like the University of St Andrews is essentially the only university with a copy). There are a few other titles known to WorldCat that are probably actually the same, but imperfectly transcribed. Nonetheless it seems pretty inconvenient.
The Centre for Computing History (in Cambridge, UK) and the Computer History Museum (in Mountainview, California) each seem to have a copy as historical artifacts.
It might be possible to get in touch with either the university libraries or one of these museums for a copy.
If you want more modern methods, the first $103\ 800\ 788\ 359$ zeros, whose imaginary part ranges in $(0, 30\ 610\ 046\ 000]$, were computed by David Platt and described in https://www.ams.org/journals/mcom/2015-84-293/S0025-5718-2014-02884-6/ (David J. Platt, Computing $\pi(x)$ analytically, Mathematics of Computation, vol 84, 2015, 1521--1535). The actual algorithm and verification is based on (Andrew R. Booker, Artin’s conjecture, Turing’s method, and the Riemann hypothesis, Experiment. Math. 15 (2006), no. 4, 385–407.) and focused on in https://www.ams.org/journals/mcom/2017-86-307/S0025-5718-2017-03198-7/home.html (David J. Platt, Isolating some non-trivial zeros of zeta, Mathematics of Computation, vol 86, 2017, 2449--2467).