Assigning Territory Accounts to Sales Team: Seeking Efficient Solutions

Hi Team, I'm trying to assign territory accounts to a team of salespeople. I have a list of our TAM, but some companies have multiple associated subsidiaries (eg: .io, .co.uk etc). Ideally I'd like to assign a salesperson a company + all it's subsidiaries + associated companies, and wondering if there's a way to do this? I've tried a few things but can't find a solution. Alternative is to sort all company names A-Z, then manually go through and find any which are likely subsidiaries/associated and assign them all to the same person. As there are 12k companies...any alternative ideas would be greatly appreciated 😅 Here is the table - https://app.clay.com/workspaces/223473/tables/t_CUQp3kuTJ5BX/views/gv_k3aZ3xriifY9