Looking to see if it is possible to create a formula to show my account number

Hello,

For work I am trying to improve an existing excel template to remove a ton of manual work, but I’ve hit a snag. The goal is to generate the account number into column B. The account is only listed as the middle six digits on certain cells (A20696 & A20710 in the attached screenshot). I know how to generate a formula to grab this number in one cell and drag it down for all cells in column B, but I don’t know how I’d get it to recognize when the account number has switched and needs to bring the new account number into the subsequent cells. I wasn’t sure if it was possible to make a formula with the existing format, but figured that it would be worth a shot to ask. Thanks in advance.