Sorry for about that I have some photos already edited in before, but I have removed in LR by my mistake, I would like to import these photos again, but all the photos are "grey" and cannot select again.
I have also un-tick the "Don't import suspected duplicates", but seem no effect:
Would like to ask is there have any step I have missed?
There is no need to import a second time (in fact, this is a bad thing to do). Exit out of the Import Dialog box (click on Cancel). Go to the Library Module. Find the photos of interest by using the Folder Panel and going to the proper folder, or by clicking on All Photographs (it's under Catalog) and then searching by File Name. Once you find them in the Library Module, you can perform any Lightroom Classic task you want on the photo.
You wrongly believe you've removed them from Lightroom. The import dialog shows they are still in the catalog. Most likely you only removed them from a collection you had selected, not from the catalog.