All that should be necessary is a few pages from the first reference below. Do not be freaked out.
I cite more to point you to where you might go next.
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Joseph Abate and Ward Whitt,
Numerical Inversion of Laplace Transforms of Probability Distributions. ORSA Journal on Computing, vol. 7, 1995, pp. 36-43.
[PDF]
(See especially the Euler algorithm summarized on page 41.)
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Joseph Abate, Gagan L. Choudhury and Ward Whitt,
An Introduction to Numerical Transform Inversion and its Application to Probability Models, in Computational Probability, W. Grassman (ed.), Kluwer, Boston, 1999, pp. 257-323 (with ).
[PDF]
(See especially the first 16 pages, with the short algorithm summary on page 16.)
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Joseph Abate and Ward Whitt,
Numerical Inversion of Probability Generating Functions. Operations Research Letters, vol. 12, No. 4, 1992, pp. 245-251.
[PDF]
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Gagan L. Choudhury, David M. Lucantoni and Ward Whitt,
Multi-Dimensional Transform Inversion with Applications to the Transient M/G/1 Queue. Annals of Applied Probability, vol. 4, 1994, pp. 719-740 [PDF]
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For more related material, see my
papers with Joe Abate
and my
papers with Gagan Choudhury