Option: Use the Find/Replace selection under the Edit menu
Option: Use the "All Transactions" selection at the top of the Account Bar. Filter listed transactions as needed (Payees, date range, etc.). Select set of transactions to be changed. Right-clicl and choose Assign Category.
Option: Create a report with the applicable transactions. Highlight the specific transactions to be changed. Clicl the Edit Button and choose the Recategorize Transactions option. (This feature may not work in current R48.xx releases to to a bug.)
also … you should pick the forum sub-section to post your questions … vs the main Root area
you're welcome
https://community.quicken.com/categories/registers-transactions-%28windows%29