merging 2 of the same checking account with "start" different dates

I recently started using Quicken after being "away" for a number of years - I tried to reconcile my checking account and it was off by $1k. when I looked at the first entry, it was a 2019 date and I have records from the bank back to 2018. I downloaded the 2018 to "start-up" 2019 date with the intent of "merging" it with the existing Quicken checking account, thereby giving me a single account with a 2018 start date. However, the 2018 file imported to Quicken as a separate new checking account and I can't find any way to "merge" it with the existing. When I imported it, the existing checking account didn't show up under "add"
any thought/help?
thanks