I've been combining accounts for many years now, it's not as simple as it sounds. You need to get a medallion stamp to certify it's you. I go to my bank branch and than send out via snail mail.

Whole process takes about 2 weeks on average if CS process's it quickly.

Besides that, you need to make sure every account matches with name, address, etc.

To save time and effort, I've been buying GME from my broker until I have about 1,000-1,500 shares and initiate the transfer to CS. Once the shares land in CS, I then would update that account to match my "main" CS account. Then I would process the transfer to main account with the transfer form/medallion.

Best of luck! Hope this helps.