Depending on the format of yourlist, you could do a search and replace.
For example, assume your tasks all have date in YYYY-MM-DD format.
Search for: “2022-”
Replace with: “#task
2022-”
Note, inserting the unicode character for the calendar sets the due date of the task to the trailing date.
In the search/replace box you will have to use your OS method for inserting this character. The unicode value is x1f4c5 and, for linux/gnome, must be typed in hex as:
Ctrl + Shift U1f4c5
-Eric