After Bellingham's departure Dortmund have signed Nmecha. However he isn't exactly playing in the same position with Bellingham mainly. On the other hand I don't see anyone they are targeting to bring to Bellingham's position in the team now. There is actually nobody I can see about their targets this summer. They are quite silent recently and I don't know if this will change either. Actually they have made a really good level of profit in Bellingham's sale. They should be able to use this money effectively.
Dortmund have great scouts so it is possible for them to find a new talent to the midfield at the age of 19 or below similar to Bellingham.