I have a PhD degree in theoretical and computational physics and a considerable experience in math and numerical methods, including computational finance models. I've done multiple financial math projects, for example the Black-Scholes model (though not specifically in the HJM model). I had a look at the HJM model's formulation and I am positive that I can implement it without difficulty. I'm an expert in Python, among some other languages. Please see reviews on my profile. I'm the author of dozens of computational research papers.
Please have a look at Computational Finance projects I've done:
https://www.freelancer.com/projects/Technical-Writing/Code-for-simulation-Scheme-Monte/
https://www.freelancer.com/jobs/Excel-Mathematics/Convert-math-proofs-Excel-formulas/
https://www.freelancer.com/jobs/Matlab-Mathematica/Write-some-Software-Matlab-Solving/
https://www.freelancer.com/jobs/Matlab-Mathematica/discrete-optimization-using-mathematica/