where can I see the person I unmatch?

Kinda can't as "unmatch" notifies the algorithm to exclude that particular profile from repeated searches.

There is a work-around, if you can remember where the profile claims to be located.

In the search field there is a box with a drop-down arrow that by default says "Near Me".
Click the arrow & type the location of the profile you want to recover into the exposed blank field.
It will give you several similarly named locations and you click the exact one you want.

Then set the distance to something like 100-150 miles of that chosen location & expand the "Age" criteria widely enough to encompass that particular profile's "claimed" age.

(Not everyone is fully truthful with the age disclosure that appears in their header - particularly women seeking an older gentleman than themselves - but men seeking younger or older also rig the "Age" criteria of the search algorithm to produce women's profiles in the age bracket they are actually seeking & to get themselves included in the search results of women seeking a man in the "claimed" age bracket.)

"Age" claims are one of the bigger problem issues on this site.
Very early on I had a woman disclose to me that she was actually 42, not the 62 her header stated, when I laughed & said "if she was 62, I was 138".
She said it was because she was seeking an older - (& presumably tamer & more sincere) - man to get a relationship going with.

Because you have changed the search parameters a re-set occurs and the profile you "unmatched" should reappear as an offering near that location.

To permanently lock it in, hit the red heart-shaped "Like" icon &/or the yellow "Nudge" icon.
If you also hit the blue "Chat" icon and send a message that profile will remain available via your "Mail" tab.