How do you become a person who likes oranges? What defines an adult baby is the desire, not the things, so if you have a desire for regression, a like of baby things, etc., you're already there. Whether you then act on those desires is irrelevant, it's still part of what you are. We know it is possible for some people to develop this interest if they care to but I think the desire is always going to be at the root of it.
I notice you've checked every profile box (AB, TB, DL, DF, Sissy, IC, Caretaker). In light of your current question, it seems to me like you should go back and reconsider some of these. A regular introduction in the Greetings/Introductions section would probably help us help you more.
As Trevor said, in order to be an adult baby you need to have some sort of desire in the first place and if you are looking to become an adult baby then there is no set way to 'become' one. Most people's desires to be babied are deep-rooted within them, and I'm sure most would agree that there has to be some intrinsic desire to want this in order to be an adult baby. That said, if you wish to become one then chances are that you already have some desire to be involved in this, and already believe that you would enjoy this. In that case you are already part of the way there
My advice would be to experiment. Think about the aspects of being an adult baby which are most appealing to you. Do you long to use a pacifier or a bottle? To be cared for? To play as a baby? Then try those things out. Try buying a baby bottle and making yourself a bottle of milk, or buying yourself some diapers to wear. It might be that you really don't like it, in which case perhaps try something else, or it may be that you really enjoy it. In that case you may want to take your experimentation further by trying something else that you feel represents part of being an AB.
If you enjoy activities which you believe are representative of what being an AB means to you, then in my opinion that probably means you are one. There are no set rules or definitions when it comes to being an AB - different members have different ideas regarding how they indulge in their AB sides and different members will have different interests. For example, some members may believe that pacifiers are a central part to being an AB, whilst other members might really dislike them. Think about the activities you would enjoy and the items you wish to use, and try them out. If after much experimentation you still do not feel comfortable or fulfilled with acting the role of AB then perhaps you are not one.
It's isn't necessarily something you become it's something you are. Buy diapers and baby stuff by all means, try it out. However if you don't like it then that may be that, this isn't for everyone and despite being a bedwetter this may not be for you. There are a lot of incontinent people who don't like the idea of adult babies.