Is there an easy way to auto-add multiple rows with the same data in a spreadsheet?

We have a tracking spreadsheet that we update twice a year. On the spreadsheet, there are repeating lines of 6/15/25 and 11/15/25. We need to add in a row with the date 6/15/26 under every single 11/15/25 line (hundreds of them). I was curious if there is some sort of formula or way to add all of these rows with the date all at once. The spreadsheet follows a pattern so the 6/15/26 line would always follow the 11/15/25 row and always be every third line in the data set.

If not, I might just be adding and copying/pasting for a while but thought I’d see if there’s a trick anyone knew of.