How to change reminder dates

I marked off a task completed later than the date I actually completed it.

I used the shortcut found here to change the date that the task was logged to July 10.

https://www.icloud.com/shortcuts/1f95607666414ebfba5359d25a08d6ee

Now that I’ve changed the date that my task was completed, my reminder for three weeks from the completion date is wrong. It is showing three weeks from TODAY, the day I marked the task as complete, rather than the day that the task says it was completed.

How do I fix my future reminders to be the correct time?

It’s really inconvenient to need three apps to accomplish basic task tracking, and it’s a huge pain to need to go into a shortcut to back date a task and then you basically lose your future reminders which is the whole point in the app for me.

If there is no other solution, I will delete the next task occurrence and when the time comes will reset a new one, but I’m going to have to just ~remember when that is. Again, not something I’m great at and the whole point of using this app.

I appreciate any help.