How to add data availability statement in Physical Review Letters?
I don't have experience with PRL, only with an APS journal(Physical Review x, where x=A-E[not all of them, only an undisclosed letter]). First of all, I would like to congratulate you, having a paper in PRL it is really something to be appreciated. For PRL, you can add supplemental material to the paper, which can be downloaded when the user downloads the original paper attached to it. As for the program which is based on a Matlab GUI, you can add a link in the body of the paper. I have seen that some authors also add links in the Acknowledgements section of the paper, where they also state that any data is available on e-mail also upon request. Also, if you used Matlab, please provide all the necessary files and the Matlab version to be used. Please use a public open access repository which will not change it's DNS in time. Moreover, don't forget that you might need to cite also Matlab as a bibtex, it might be a necessity when using this software product (see the copyright files when you installed this software on your computer).