A few of my floor tiles are popping up, but I can find the same color tile anywhere.
Is it possible to reuse the old tiles? If yes how?

Is this ceramic or vinyl. Either or you can reuse the tiles.

They need to be cleaned off and old glue on floor scraped up and the back of the tile. For the tile I would simply use a widget/razor scraper for that/ Wear eye protection when using a widget.

Look for an all purpose floor/tile adhesive if its vinyl. There are certain adhesives for below grade floors because of moisture.