What do you mean, "just started to fail"? It's a very simple tiny push-button behind the silver fascia.
Just in the off-chance you've forgotten, the remote key must be on your person, or within 5 metres of the car, and options for touchpad opening/closing (which doors and with what feedback, if any) must be selected through the Vehicle Settings submenu on MyLink.
You do not necessarily have to press the driver's side touchpad to enter/exit the car. Unless you select (through the MyLink interface) that the driver's door only will unlock when the touchpad or remote key is used, then any touchpad around the car can also be used to lock/unlock it.
Failing that, a quick squirt of WD-40 and allow to penetrate. Keep WD-40 away from the paintwork: use a towel or rag held under the door handle during squirting, and keep it there until it the carrier has evaporated.