I like to run a fair bit myself and would really recommend you not worry about it. Just enjoy the run.
Aside from a little vaseline I prefer to let things do what they want to do down there, otherwise after a few hours of running I tend to have problems with chafing. While you’re going to have a little shrinkage, and it may not be the best thing for the ego the health benefits are going to far outweigh any of the drawbacks. Besides, the increased cardiovascular fitness should improve penile function, which ain’t bad!
There are times to train for running, and there are times to train for PE.
*You're in the right place – all the information you could ever need about PE is only a forum search away!*
Take your time, pick a simple routine you can stick to, and be consistent in your efforts. Patience is the key.