Edge of countertop is coming loose but it’s not big enough to get new glue under it.
Try a small amount of glue on a piece of cardboard and try to slip glue under area with that. Don't leave in the cardboard.
Contact cement is what is used to secure laminate for countertops to the substrate (plywood) and can be purchased in small bottles. A small disposable brush or even a cotton swab can be used to apply the cement to both surfaces, if possible, then clamp or weight it to dry. Hope this helps!
Carefully pull the piece off so you can get a good amount of cement onto each surface with a small brush, once tacky, press it on and run it over with a rolling pin. If possible, clamp it, if not, continue to revisit every few minutes with the rolling pin until dry. If the present glue is failing, it will likely continue and you will be dabbing bits of glue with a toothpick until the cows come home.
Iron over it. The glue that is dried on it should liquify and reattach it.