Cleaning Stock Register After 25 Years

$$Elu3030

After 25 years my stock registers are chaotic from neglect other than what is downloaded off the internet. Stocks long since sold, disappeared (crash of 2008), mergers, forced reconciliations, etc. One stock remains in my IRA and it pays dividends (reinvesting) as regular as a clock. Question: how to sever this account from Quicken without creating chaos on the whole system?

Then manually entering the dividends into the new register.