Find an area where you have to disassemble large problems into small ones, where you have to plan a few steps of the solution. Any knowledge area will do. Writing was suggested in another comment, it's a good playground. As is programming, where there is ample literature of puzzle problems to solve. Algebra, if you are so inclined although, beware, it veers a bit into the abstract. There are physical hobbies with that characteristic too: anything involving woodwork or building stuff out of parts (or disassembling and reassembling, like mechanics).
Having picked up a hobby, apply the hours. Start with stuff you can do, don't overshoot complexity. Then, evolve from there. As with all new activities, embrace failure. Don't just accept failure, expect it, learn from it, step on past failures to evolve.
P.S. I can't imagine not having an inner monologue, or its dual, spatial imagination, but a relevant part of the population doesn't have either, with no ill effects on the thought process. It's amazing, to me, but it seems they are not required for thinking.