If this is the first year you are using this spreadsheet, open the spreadsheet, and click on the 'File' tab in the upper left below the spreadsheet title. Scroll down to 'make a copy' and use that option.
If you have this spreadsheet from last year with 2025 already filled in, then you can copy the '2026' tab directly to your existing document by going to the '2026' tab, clicking the little arrow to the right of the tab name, and scrolling down to 'copy to' and select 'existing document' and then finding your document. (be sure to rename the tab you just copied to limit it to just '2026'. Same is true for any old tabs. The spreadsheet only interacts with other tabs when the tab names are restricted to the year.)
rob