Welcome to a great site for help and inspiration. We are glad you joined.
Dog Food? Well, what are you feeding your pup now? And what were the parents being fed? I guess you would start there. When we got our girl she was being fed a low quality dog food but after joining the Forum we were given the good advice to check out the Dog Food Advisor and it was a blessing. People have no idea about just how nutritious or non-nutritious their dog food is, but looking it up on the Advisor will open your eyes.
You are growing what will be a very large dog, and good food now will go a long way to great health in the future. Try and pick something in the upper ranges, 5 and 4 star products with good reputations. Many pet food stores will have trial bags of the better foods so that you can find one that is both tasty and good in quality. We experimented for quite a while with the same manufacturer and settled on a fish based food, but they have other products and every meat group is represented. And here is something to remember, all breeds of dogs have sensitivities, you might find out that yours doesn't do well on chicken (a lot of Mastiffs don't) and so you may have to settle on fish or beef or veal or....the list goes on. Also, when changing between foods because you've noticed a sensitivity it's hard to go cold turkey, better to wean away from it with decreasing quantities.
Some of our EM owners will jump on with specifics of the food that they rely upon, but also do your own homework, go to the Dog Food Advisor
https://www.dogfoodadvisor.com and you will find a wealth of reliable non-partisan knowledge. Nobody can "pay" to get a good review there so you will always know you are getting the best advice nutritionally.
Other than that, find some basic training courses that you can take with your pup, it will pay dividends in the future...BIG DIVIDENDS. Every dog should know the basics and should be able to come, stop, hold, drop, bring, sit, lay down. A big dog NEEDS to know these to be a successful Big Dog. And with them, you will be a successful Big Dog Owner.
And, Again, Welcome To Our Pack!
