Most people just communicate online with microtask workers.  But I would definitely recommend looking into a platform that uses chat and video so that you can communicate and see their face.  It'll make it more like hiring a personal assistant.  It also works well if you need someone to be available when you have questions about your diet.  For example, do you have a lot of food in your house that you want to avoid?  Would it be really helpful if you could get help figuring out which foods to eat, how much to eat, and so on?  For some people, it helps a lot to have a person to have a face-to-face chat about that.
assistant
They'll work remotely.  So you might want to find someone who's in your general area, and make sure that they're familiar with your diet, as well as some basic nutritional information about what's healthy.   There are also services that could do a lot of the shopping for you, so that you don't have to be the one to buy the food.  You could also make some copies of your recipes and post them to a shared file online, so that anyone can see what you want to eat, and how you want to make it.
assistant
I want to lose 15 lbs, what's the best way to do this?
user
Well you could do some research and come up with some weight loss strategies that sound like they might work for you, or you could ask someone to take over your diet for you, so that they'll make decisions for you while you're doing things that you really like.
assistant
How do I find someone like this?
user
I know that you probably don't want me to really act as a dietician.  But here's a link to a site where you can ask other people who have specific skills to help you.  This is called a “micro task” site, and you're probably familiar with some of them already, like freelancing sites like Upwork.  It's a different way of getting help than you might expect.
assistant
Will they come to my house?
user