First, make a backup of your save
From what I googled, you will need a Ren'py save editor
Open the savefile with it and find the variable "store.nia_alert00"
Change it to false
Save the changes and try loading that save
You might have to do that process again, but set the variable to true after triggering the event
I haven't tried this yet, but I will let you know when I do
This site has some options for save editors. Again, I haven't tested myself yet
https://arceusx.net/renpy-save-editor/#What_Ren’Py_Save_Editor_Is_Used_For